Screw Guide

Screws - the great advisor

Whether with a hobby craftsman or an experienced professional - the subject of screws always raises many questions. Which screw types are best suited for which application? What effect do the thread types have on the benefit? And what distinguishes a wood screw from a metal screw? 

In order to ensure the best result for each construction it is important to use the right screws. This is the only way to create the best connection and a stable component for workpieces of all kinds. In the following guide you will get a comprehensive overview of screw types, the fields of application and the structure of the individual screws. This makes it easy to choose the best screws for each project. 

Content

Screw types according to thread

Special screws

Screw head: When to choose which?

Screw material

How many screws are needed

Chipboard screws

The chipboard screw for fast and flexible processing.

Wood construction screws

The powerful, approved screws for structural timber construction

Fully threaded screws

The fully threaded screws with intelligent solutions for demanding constructions

Terrace screws

The high-quality screw assortment for the professional terrace assembly

Special screws

The high-quality fischer screw range for special applications.

facade screws

The special screw assortment for fixing wooden facades.

Drywall screws

The extensive range of drywall screws for fastening drywall panels to all types of substructure.
 

Screw types – an overview by threads

Screws can be classified by different criteria. Laypersons tend to pay attention only to the area of application. If, for example, wood is to be used, one starts looking for wood screws. It quickly becomes clear, however, that there are again countless types of screws within this category. Which model is the right one depends here among other things on the type of wood. Do you work with a particularly hard or a particularly soft wood? Would you like a countersunk head for the screw? Do different types of wood or wood materials have to be joined together? Even experienced craftsmen quickly reach their limits here.  

Therefore it is advisable to take a closer look at the threads of the individual screws. The thread types are particularly suitable for certain areas and allow a clean and problem-free work with the workpieces. 

Metric threads in particular are generally divided into external and internal threads. A fastening piece with an external thread can be accommodated by a matching internal thread. Self-tapping or self-drilling screws generally do not have threaded mating parts (such as nuts or threaded sleeves) - the fastening is secured by the connection between the screw and the screw material.  

The most important technical terms in the overview:

  • Thread outer diameter or nominal diameter: designates the maximum thread width in longitudinal section of the screw or the maximum outer diameter
  • Thread Core Diameter: Designates the smallest diameter at the inner thread edge.
  • Thread pitch diameter: Distance between the profile center lines of the two thread sides.
  • Flank angle: Angle between two thread flanks.
  • Thread pitch: Distance between the tips of the thread flanks after one revolution.
  • Thread pitch: Circumference of the entire helix of the thread.Only the area of the screw with the spiral notch is designated as thread. If there is a smooth area above it, it is called the shank.

Only the area of the screw with the spiral notch is designated as thread. If there is a smooth area above it, it is called the shank.

Screws with metric thread

The so-called metric ISO thread is a standardized thread that uses a metric dimension. The metric thread has a flank angle of 60 °. The screws with metric ISO thread are used globally. In the past, metric threads with slightly different dimensions were used. The inch threads were added. These have been replaced by the metric thread in most countries. Thus, there are still isolated screws with inch threads.

Screws with metric thread were standardized in 1996 via ISO 1502 (DIN: Metric ISO thread general application). They are described in the DIN standards DIN 13 and DIN 14. 

The screws with metric thread are offered as a pairing of screw and nut. Within the screws, a distinction is still made between models with standard thread and fine thread. The flank angles and the thread pitch of the fine thread are smaller than those of the standard thread. Screws with fine thread are very well suited for workpieces where there is little space for screwing in the screw. The reduced flank distance increases the number of existing thread cuts and thus the holding of the screw. 

In general usage, screws with metric threads are also called screws with metal threads. This is also the case if the screws are made of plastic in part or in whole. The designation metal thread indicates that these screws are only used together with a preceding nut. In comparison, universal screws or self-tapping screws, for example, cut their own threaded hole into the material. 

In addition to the different types of thread, there are also several types of flank. These can each be used within the thread forms. For example, there are screws with metric threads that have different flank shapes. The flank shapes often limit the individual application area: 

  • Pointed thread - suitable for precision mechanics and general use
  • Saw thread - as movement thread
  • Flat thread - formerly used as motion thread, today hardly existing  

Screws with split thread or double thread

The double-thread screws are used especially in timber construction. They are used as a variant of the full-thread screws for connections or reinforcements as well as for the fastening of on-roof insulation systems, especially when using pressure-soft insulation materials. This special type of wood screws convinces with an easy assembly and high efficiency.  

The thread enables axial load transfer. In direct comparison to a classic partially threaded screw, a higher tensile load is transferred and a high compressive load is optimally absorbed. The screw uses two threads with different pitches. These compress the component when screwed in. It is therefore not necessary to pre-tension the component to create an optimized design. The screws with double threads are therefore not only highly resilient, but also economical. 

These screws usually have a cylinder head that can be sunk almost invisibly into the wood. At the same time disassembly is possible without any problems. It is not a countersunk head - you can screw in the screw without splitting the wood. If the fire protection is relevant for the building project, the screws can be completely countersunk in the wood and covered with a cross wood / cone plate and thus already meet some requirements of the current fire protection regulations.   
fischer spacer screw ASL with double thread

Screws with full thread

Fully threaded screws are used in timber construction. The thread of the screw usually extends over the entire screw length. It starts directly under the screw head. The thread is able to absorb high tensile and compressive forces and distribute them evenly. This type of wood screw is therefore particularly suitable for construction projects in which wood components are under permanent force. These screws are also very well suited for the reinforcement of wood components. Larger dimensions are used for heavy-duty connections and reinforcements and almost always have a European Technical Assessment (ETA) with the indication of the respective load-bearing capacity. Bolt manufacturers also often offer design software for the calculation of the load capacity of the present connection. 

Special chipboard screws are offered for the screw connections of wood-based panels (such as chipboard or OSB panels) and all types of wood as solid wood. These are equipped with a full thread or also with a partial thread. These screws have a self-cutting thread or even a drill point. They can be screwed into soft and mostly also into many hard wood types and chipboards or MDF-boards without the need for pre-drilling. For the processing of full-thread screws with countersunk head, make sure that this is screwed into the wood flush with the surface. Deeper screwing in can split the wood.

Screws with partial thread  

Wood screws are available with full thread or partial thread. Partially threaded screws are ideal for creating a secure fastening between wooden boards and wooden beams. A screw with partial thread has a thread-free area underneath the screw head, which is called the shank. The shaft length should at least correspond to the thickness of the wooden panel to be fastened, so that the two components to be screwed together can be pulled together cleanly. 

Partially threaded screws are also offered with countersunk head. Alternative head forms are the plate head or the hexagonal head with an integrally formed U-washer. Wooden panels on walls or wooden beams for terraces can be screwed together cleanly and evenly. If the screw is not equipped with a self-tapping thread, a pre-drilling is necessary.  

Screws with internal thread

The screws with internal thread are used particularly frequently in furniture construction and thus in wood processing. 

Screws with an internal thread are usually supplied with a suitable counterpart. There are also models that are suitable for screwing with DIN standard threads. The screw has a classic external thread with which it is fastened in the workpiece. At the same time there is a hollow internal thread that can accommodate another screw.  

Some manufacturers offer combinations of the two mating parts, which are only adapted to each other, not standardized and therefore cannot be combined with other parts. This is often the case with special furniture screws. This type of screw is used to securely connect individual furniture parts. As a rule, however, they are metric standard threads.  

The internal threads are also often used for pipe threads. These are not screws in the classical sense. The threads are applied directly to the ends of the pipes and allow a simple connection between pipe sections. Both internal and external threads are offered here. The pipe threads can be self-sealing (conical or tapered) or cylindrical. In this case they are not self-sealing and require an additional sealant for the connection.

Screws with inch thread

Globally, metric screws are the most common utility screws. There are some markets, where inch screws still hold their ground. Especially in the USA, inch screws are widely used. In comparison to a metric screw, the main difference between a screw with inch thread is the underlying unit of measurement.

One inch corresponds to 2.54 cm. If you want or need to work with inch screws, it is important to make the correct calculation before buying screws. This applies to screws with fine and coarse thread. 

There are various types of threads for inch screws. The following are the most common on the worldwide market: 

  • UNC - US-American standard thread. The coarse thread was formerly known as NC.
  • UNF - US-American standard thread. The fine thread was formerly known as NF.
  • British Whithworth thread (e.g. BSP, BSW and BSF) - Whithworth threads have a flank angle of 55°. The metric screws have a flank angle of 60 °. 

UNC and UNF threads also have a flank angle of 60°, but have a different diameter than the metric screws. Therefore, metric screws, American inch screws and British inch screws are not compatible with each other. 

Regardless of the thread type of the inch screws, the length of the screws is always indicated in inches or mm. The thread diameter, on the other hand, is only given as breakage. Inch is described with the special character ". A thread with "¼" therefore has a diameter of 6.35 mm (= 1/4∙2.54). 

Screws without thread

There are no screws without thread in the true sense of the word. This type of screw refers to pairs of screws, which are composed of a normal screw and a screw with internal thread. The screw connection is thus secured by bringing the two parts together. 

These models are available in different lengths and designs. So you will find offers for each screw head. Some counterparts can be screwed into the screw without external thread, others come in the form of a nut and are turned at the lower end via a short threaded piece.  

Again, these are mainly screws from the furniture industry. The head of the screws often disappears flat in the pre-drilled holes. Screws without thread with a short counterpart usually use a fine thread. This ensures a high degree of safety despite the short connection piece. 

Cheese head screws

 The cap screws, also known as socket head screws, are used in areas with special design requirements. If the screw head is difficult to access due to the construction of the workpiece, hexagon socket head screws are the right choice. In most cases, the workpiece has identical dimensions as the screw head. The specific product requirements that the cylinder head screw must meet depend on the component. 

The range of cylinder head screws is correspondingly extensive. Models with a low head height or versions with a slotted drive are available. In addition, cylinder head screws are available in accordance with the metric DIN standard. You also have the choice between full thread and partial thread.  

It is possible to have special designs manufactured. The dimensions of the screw are then perfectly adapted to the workpiece to be machined. However, this offer is rarely used in the private sector. The screws are offered in usual standard lengths: 

  • 0 - 45 mm
  • 46 - 75 mm
  • 76 - 110 mm
  • 111 - 200 mm

They are versatile and are particularly suitable for joining different metals such as galvanized and ungalvanized steel and stainless steel. 

Cylinder head screws in use

Screws with drill tip

A further speciality in the screw assortment are screws with drill tip. These screws have a pronounced tip, which - as the name suggests - is suitable for drilling into a workpiece. The basic shape is similar to that of a classic drill bit. Usually the drill tip has two cutting edges. You can use a screw with drill tip very well for joining metals or plastics. This type of screw is regularly used for fixing window fittings. 

The screws with drill point can be found in various design combinations:

  • Metric thread
  • inch thread
  • Various drives
  • Different head shapes

The starting point for the tool, the bit, is named as the screw drive. The best known forms are the slot drive (bad when used with electrical screwdrivers, because the centering is missing and the screw wobbles when screwed in) and the cross slot drive. Furthermore, there are among others the hexagon socket, the external hexagon, the TX (or Torx) inner star or the square drive.   

fischer Powerfull with drill tip. The drill tip enables screw connection without pre-drilling and provides guidance when screwing in.
 

Special screws

Special screws are used especially in industry and in the skilled trades. These are optimized for the special features of various workpieces or constructions. Whether a very high tensile load has to be carried or the screw within a construction is difficult to reach - with the right special screw the best solution is quickly found.  

It is possible to have screws made to measure. A procedure that is primarily used for large projects. For the private sector or for use in small and medium-sized companies, the costs for custom-made products are too high. Therefore there are some special screws which are offered in standard form. 
 

Adjusting screws

Adjusting screws are used in connection with wooden components. Underneath the screw head there are threadless grooves. If an adjusting screw is screwed in, these grooves get caught in the workpiece to be attached. This provides a good hold in the workpiece to be attached. Even if the screw is then unscrewed slightly counterclockwise for adjustment, the connection remains stable thanks to the adjustment grooves. 

Another advantage of adjustment screws is the self-cutting thread. It is not necessary to drill a complex pre-drill.   

Hanger bolts

The hanger bolt has a wood thread at one end. The other end has a metric thread. The hanger bolt is used, among other things, to secure a workpiece with a nut on natural stone, wood or concrete. 

Wrench screws

The wrench screws also fall into the category of special screws. These are screws that can be fixed with a wrench or a socket wrench. The wrench screws correspond to DIN 571 and are also in use under other names: 

  • Hexagon head wood screws
  • Eternit screws
  • Vienna screws

The thread of a wrench screw does not start directly below the screw head. There is a smooth shank. The partial thread ensures that a high pressure is created between the components to be connected. If, for example, two boards are screwed together, the lower wooden component is pulled securely against the upper one.  


The key screw is a classic wood screw. The hexagonal screw head makes retightening easier. The screws are also available in stainless steel.  When used correctly, key screws must always be pre-drilled in two steps in the wood. 

You can get the key screws among others in galvanized and hot-dip galvanized steel.  

 

Safety screws

The screws therefore differ from commercially available screws primarily by their special drive. You can buy the matching bits in a hardware store, should it be necessary to open a special screw. The most common screw drives for special screws are the following:

  • Hexagon socket with pin
  • Torx with pen
  • Interior variety
  • Disposable Slot
  • Tri-Wing
  • Torq Set
  • Pentalob
  • Clamp (two-hole drive)
  • Bristol

A disposable screw cannot be loosened with a normal tool. The drive flanks are flattened in the return stroke and do not provide a support surface for a tool. If it should be necessary to disassemble it, there are special tools such as a left-hand screwdriver. 

Special screws are always used when loosening of the screw connection should be prevented as far as possible. A classic example are vehicles in public transport. Companies that manufacture electrical appliances increasingly rely on special screws to prevent customers from carrying out dangerous repairs themselves. Children's toys that use potentially dangerous components inside also use special screws. 

Depending on the type of safety screw, models are available with lens head, flat head or countersunk head.  

Self-tapping screws

A self-tapping screw can cut its own thread into a material. This type of screw is used in many areas, as it is suitable for processing wood, metal and plastic. 

The screws are offered in two versions: Thread-cutting screws and thread-forming or thread-rolling screws. The thread-forming screw has a blunt end. A thread-forming screw has a pointed end. Accordingly, both types are processed differently.  

To insert a thread-forming screw into a material, a pilot hole is required. This is especially true when the tapping screw is used in metal sheets. On very thin sheet metal, you can mark the drilling location with a center punch, which makes it easier to drill into the workpiece. For thicker sheets and steel, however, it is essential to carry out a proper pre-drilling. Always choose an attachment for pilot drilling that is approx. 2 mm smaller than the screw. However, for smaller or larger diameters, make sure that the diameter for pre-drilling is precisely specified. 

A thread-cutting or self-tapping screw with a point is screwed into the workpiece without predrilling. These screws are very popular in woodworking and furniture construction. They can be inserted easily and quickly in very different materials. At the same time they can be disassembled at any time.  
 

Screw head: when to choose which?

Not only the thread plays a role in choosing the right screw. The screw head must also be considered. Basically, it is of course relevant that you have the right tool for the screw head and the screw drive at hand. But beyond that, the different heads are more or less suitable for certain areas.  

Classical screws for domestic use have a flat head with a slotted or cross drive. However, slotted screws are becoming less and less important, as the lack of centering of the screw bit when screwed in can often cause slight injuries or at least trouble. But for both screws almost everyone has the right tool. Simple screw connections between workpieces or for wall mounting can be easily implemented. For a good load transfer in solid or drywall construction, the appropriate dowels are also relevant. You will find all important information on the subject of dowels in our large dowel guide (link to dowel guide). 

The following is an overview of the most common screw heads and screw drives as well as the relevant areas of application. 
 

Screw drive/ screw profile

The screw drive or the screw profile designates the projection on the screw head that is inserted into the tool (bit and then bit holder). Usually, a manual or electric screwdriver is used as a screw-in tool. Nowadays it is mostly a cordless screwdriver.  

There are far more than 100 different screw drives. Many of them are used in industry or in house building. Others are country-specific and are therefore regionally limited and most frequently used. Globally seen the slotted, the cross slotted (Philips) and the pozidrive drive (cross recess) are particularly widespread. Also the inner star TX- drive or also called Torx are very common. 

There are many screw drives as inner drive and outer drive. For example, a 3-edge nut is placed over a triangular drive and the 3-edge bit is plugged into a triangular drive. When choosing the screws, therefore, make sure you take into account which tool you have available. A comprehensive tool kit ideally contains the respective bits and nuts. 
 

Phillips and Pozidrive

One of the oldest and also best known screw models is the Phillips screw. In private households it is the most commonly used screw drive. Before its introduction, the simple slotted drive was the only available screw type. The cross-head screw was a further development of this basic form. An easier power transmission could quickly convince the users.  

Around 1920, the Philips drive was then introduced to the market. Basically, this was also a cross recess drive, but the torque was considerably optimized. In addition, the design of the drive allowed automatic centering of the screws. A further improvement finally led to the Pozidrive drive. The very good power transmission of this model makes work much easier. For bolting with normal requirements, the Pozidrive screws are the best choice in private households. 

Torx - the drive for the professionals

A Torx drive is a registered brand product. However, there are also no-name versions on the market. The Torx drive is very popular, especially in the professional trade. It is an optimization of Pozidrive and Co. The star-shaped drive offers a number of advantages in processing: 

High power transmission
Stable centering
No slipping away
No turning back

Hexagon - the robust classic

With a hexagon head screw, the screw head is also the drive. The big advantage of this drive is that the screw can be gripped from all sides. Therefore it is also suitable for mounting in places that are difficult to access.  

Today, hexagon head screws are also increasingly used as decorative elements in furniture construction.  
The different screw drive types.

Screw head shapes

The choice of the suitable screw head determines the functionality and the appearance. The selection is extensive, and the individual heads have very different advantages and disadvantages to offer:

  • Flat round head (e.g. for carriage bolts): This screw head has no separate drive, and the bolt is fastened by means of a nut. Ideal for creating particularly secure screw connections, for example on a playground equipment.
  • Lens countersunk head or mushroom head: This screw head is a true classic. The countersunk part of the head is countersunk in the attachment and the upper half of the "lens" shape protrudes over the attachment. This head shape is often chosen because of the optics. The rounded head also reduces the risk of injury.
  • Pan-Head or half round head: This head has a flat lower head shape and is not recessed in the attachment at all. It protrudes over the attachment at full head height. This head shape is almost always used in combination with metal sheets or plastic attachments. Practically never, with attachments made of wood.
  • Countersunk head: The screws with countersunk head are used in all forms. Wood screws, metal screws or special screws use this design. The advantage is that the head can be countersunk flush with the surface of the material. In addition, the countersunk head is offered with all common drives from Torx to cross recess.
  • Disc head: A wood screw is often equipped with a disc head. You do not need to use washers for these screws to ensure even power transmission. The disc heads are visually attractive and are therefore often used in wooden constructions. Due to the increased head diameter, the screws can transfer higher loads in wood than e.g. countersunk screws, as the resistance to head pull-through is significantly increased.
  • Cylinder head: Cylinder head screws are widely used in metal construction. They can be used from the side and from above. They are ideal for providing the best possible performance in industrial environments.

Screw length

In order to securely connect workpieces together, the screw must have the appropriate length. If it is too short, no secure hold is provided. If it is too long, it protrudes from the workpiece. Depending on the head shape of the screw, the length is measured slightly differently. 

A screw with countersunk head is measured in its entire length - from the beginning of the head to the tip. A screw with an overlying head, for example a pan head or disc head, is dimensioned from the underside of the head to the tip. When purchasing a screw, consider not only the thickness of the workpiece, but also whether you are using a dowel, washer or nut. There are also many combinations of length and diameter of screws.  
 

Screw diameter

The screw diameter is measured at the thread. The value indicates the widest thread diameter of the screw. The diameter of the screw is relevant in many areas. If a pilot hole is important, you can select the correct size for the drill using the screw diameter. 

Especially with wood screws, an incorrectly selected diameter can cause problems. If the screw is too thick, the danger of splitting in the wood is too high. Therefore, in general, always pre-drill in wood for wider screws, even if the thread is self-tapping, unless the edge distance and the wood thickness and width are large enough. 

 

 

The screw material

The offer for different screw materials is constantly growing. There are even mixed types that use several materials. However, since certain conditions such as tensile strength or corrosion protection usually play a role, some materials are used particularly frequently: 

  • Stainless steel
  • Steel (often hardened) and usually galvanized and passivated or hot-dip galvanized
  • Plastics
  • Aluminium
  • Brass

Stainless steel screws and steel bolts provide high strength. Stainless steel screws are extremely weather resistant. In addition, they are inexpensive to manufacture. Brass screws are nice to look at and offer even better corrosion protection than e.g. galvanized steel screws. Steel screws and other metal screws are used in private and industrial environments.

Plastic screws are often marked PA: polyamide. These screws are light and cheap to produce. They also have a high flexibility. Unfortunately, they are not particularly temperature-resistant and have little load-bearing capacity.  

 

Which screw for which material?

You have the choice between wood screws, metal screws and also universal screws. In addition, there are special designs within the screw types that are optimized for specific applications. From the thread to the material to the drive, these screws are adapted to the individual conditions of each workpiece. The strength class also plays a role. A metal screw is exposed to greater stress during processing than a wood screw, for example. In the following the special features of some types of screws for certain materials. 

Screws for gypsum fiberboards

Gypsum fiber boards, also known as Fermacell boards, are used in dry construction whenever the construction must meet high standards. The stable boards are thus well suited for high shear loads and fire stress. In comparison to plasterboard, the gypsum fiber boards are heavier and at the same time much more resilient. 

Fastening to a substructure requires a little effort. Especially the choice of suitable screws is important. Special drywall screws, the Fermacell drywall screws, have a self-tapping tip and are used without pre-drilling and without dowels. The thread of these screws is often a double thread in a HiLo version (one thread protrudes slightly more than the other over the core diameter of the screw). The screws are offered loose and taped (for faster screwing in with magazine screwdrivers for inserting many screws in series).

Screws for plasterboard

The plasterboards, also known as Rigips boards, are light and easy to install. They are also very cheap to buy. The sheetrock board is suitable for the quick covering of walls and ceilings. These are also known as dry construction walls or ceilings. Special drywall screws are used to fix the panels to the metal or wooden substructure. In a relatively soft material such as wood, it is best to insert the screw with a coarse thread. In substructures made of metal (for metal stud walls), drywall screws (or also drywall screws) with a fine thread are used. As a rule, no pre-drilled holes are used. These screws are also offered loose or taped (for faster screwing in with magazine screwdrivers for inserting many screws in series).  
 

Wood screws

The thread of a wood screw is optimized to be easily screwed into all kinds of wood. It exerts a low splitting force, which is especially advantageous for small edge distances and for thin wood panels as well as for harder wood types. If the screw is not equipped with a self-tapping thread, you should always pre-drill the material (e.g. in the case of key screws according to DIN 571). If you are connecting different materials, for example steel and wood, it is also important to pay attention to the type of screw head. If the screw head rests on the steel and the thread is screwed into the wood, a model with countersunk head is not so well suited, since a countersink must be provided in the steel attachment. In this case, a plate or hexagonal head (the latter also with a formed washer), as with a normal metal screw, is the right choice. 

Screws for MDF

MDF boards are medium density fibreboards, which are pressed from a mixture of wood, glue and water. The board does not have a grain pattern. Never screw the MDF board directly, it is better to pre-drill all holes in the board. Without this pre-drilling, the risk of splitting is too high for the board.

Thick MDF boards can be fixed well with a partial thread.

Chipboard screws

The chipboard screw can be a universal screw or a wood screw with countersunk head. The material does not have to be predrilled. The sharp tip of the screw for chipboard cuts directly into the material without much resistance.

Sheet metal screws

Self-tapping screws have a hexagonal head, an oval countersunk head or a pan head. There are no models with countersunk head. The thread is specially hardened and able to be screwed into the material without pre-drilling. The self-tapping screw is made of robust steel or stainless steel, and you can get models with cross-head or hexagonal drive, among others. Many self-tapping screws also have a drill tip.  

Screws in concrete

If you want to sink screws into concrete, there has been a popular alternative to metal expansion anchors, heavy-duty anchors, etc. A concrete screw is screwed directly into the material without the use of anchors, without losing any load-bearing capacity. The thread of the screw is provided with a special serration, which cuts an additional internal thread in the drill hole. In order to use the concrete screw safely, only a pre-drilling is required. Then the concrete screw made of steel or stainless steel is simply tightened with an impact wrench (tangential impact wrench) or, in exceptional cases, by hand.

Drywall screws (plasterboard or gypsum fiberboard screws)

Drywall screws (or drywall screws) are mainly used in drywall construction. There are versions with or without drill tip. The drill tip is especially suitable for use on metal substructures without having to pre-drill there. You can get screws with fine thread (for metal substructures) and coarse thread (on wood substructures). Many models are also available as magazine screws. Screws with double or HiLo thread (one thread protrudes slightly more than the other over the core diameter of the screw) are ideally suited for good workmanship and load-bearing capacity in gypsum fiberboards (Fermacell boards).

Which screws are suitable for dowels?

If you want to use dowels, screws and dowels must be matched. Although it is possible to buy pairs of screws and plugs ready to use, it is often easy to put together the two counterparts yourself. The choice of plug is determined by whether you drill or fix to a wall or ceiling. The material of the substrate is also important. For aerated concrete, for example, you need a different plug than in concrete. Basically, you can get universal plugs, special plugs and cavity plugs for the combination with screws.

You get the correct screw length by adding the plug length, the thickness of the work piece to be fastened and the screw diameter. You can also easily determine the appropriate screw diameter:

  • 6-pin dowel Ø6 mm - Drill 6 mm for the hole - Screw diameter: 4-5 mm
  • 8-pin dowel Ø8 mm - Drill 8 mm for the hole - Screw diameter 4.5-6 mm
  • dowel Ø10 mm - drill 10 mm for the hole - screw diameter 6-8 mm
 

How many screws are needed?

You are planning a construction project and want to order all materials in time? In the following you will get an overview of the number of screws you need for various connection problems.

How many screws per decking board?

In order to screw a decking board securely, usually two screws per board and crossing point with the substructure are used. With particularly long planks, the number of screws depends on the number of the underlying construction beams. The distances of the beams in the substructure must therefore be designed so that the deflection of the decking boards is not too large and the load-bearing capacity of the decking boards is given.

How many screws per OSB panel?

OSB boards are available in the standard dimensions 2500 mm x 625 mm or 2500 x 1250 mm. In addition, the boards are available in different thicknesses. They are easy to install and are very suitable as a vapour barrier, among other things. If the boards are screwed to a substructure, the center distances between the beams or uprights should not exceed 62.5 cm. Some boards (so-called installation boards) have a tongue and groove all around. If the panels do not have a static load-bearing function for the stability of the building, a general screw spacing of 10 - 15 cm can be provided at each linear intersection with beams or uprights of the substructure. 

How many screws per m2 plasterboard?

To guarantee a secure hold for plasterboard, the distance between the screws should not exceed 25 cm. Depending on how the substructure is constructed, more or fewer screws are used. The distance to the edge of the board should be around 15 mm. In general, it is better to use too many screws than too few. This is especially true for fixing panels to the ceiling and for thin panels.  

Screws - Strength classes

The strength class of a screw is indicated for metric screws made of hardened steel by a numerical combination of two values. The two numbers are simply separated by a dot. The first number denotes the index value of the tensile strength / 100. The second number denotes the index value of the yield point as a ratio of the yield point to the tensile strength:


Tensile strength: What is the maximum tensile force the screw material can transfer without breaking? The screw can be permanently deformed (elongated). The unit is N/mm².
Mating limit: This is the stress in the screw (unit N/mm²) up to which the screw behaves elastically, i.e. it returns to its original length after loading.

Loosen broken screws

If the screw drive is worn out, it is not easy to loosen a screw. But with a few simple tricks you can also remove stuck screws:

  • Remove slightly protruding screws with a gripper
  • Place screwdriver with a rubber preserving in the worn drive (especially for cross recess)
  • Slight wear can be eliminated with an impact wrench and the appropriate bit
  • Use a special screw extractor set to cut a counter-rotating thread in the screw head

Screws without pre-drilling?

Whether screwing without pre-drilling is possible depends on many factors. Among other things, not every thread is suitable. If a wood screw is not equipped with a self-tapping thread, you cannot avoid pre-drilling. Especially if the wood is quite thin and you work close to the edge with a thicker screw. Otherwise the danger of splitting is too high. 

In concrete you always have to pre-drill, in metal you almost always have to pre-drill. Only thin sheet metal and plastic can be worked very well with the appropriate special screws, even without pre-drilling. If screws with drill point are used, then it is also possible to screw into thicker sheet metal without pre-drilling.

Derusting screws

If rust has formed on a screw, there are various ways to remove the rust. Special rust converters are particularly easy. These chemical agents are available as gel, paste or spray. Depending on how severe the rust attack is, chemical rust removers are very suitable for large and small surfaces. If a small metal screw is affected by rust, an old household remedy can often help: simply treat the surface with vinegar or citric acid. 

Electrolysis is a good method for dissolving large amounts of rust without much effort. To do this, fill a plastic bucket with water and add four tablespoons of sodium bicarbonate per liter. Use a piece of steel as anode. For the sacrificial anode use a piece of magnetic material that is in the water. Connect the positive pole of a charger to the sacrificial anode. Connect the other pole to a stainless place on the metal piece to be treated and immerse it in water. It may take up to 24 hours for the rust to completely dissolve. 
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