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      • Published 31 May 2023
      • Last Modified 29 Aug 2023
    • 13 min

    Self-Tapping Screws Guide

    How to choose the right self-tapping screw for your project? Our guide explains the different options and their uses.

    Self-Tapping Screws Banner

    Reviewed by Maxwell Brown, Technical Support Engineer (April 2021)

    What is a Self-Tapping Screw?

    Self-tapping screws are different from traditional screws as they tap their own threads when screwed into plastic, wood, or metal. Self-tapping screws are usually split into two variants - thread forming and thread tapping.

    Thread Forming Screw

    Thread Forming Screws

    A thread-forming screw has a specific thread pattern that creates a thread during insertion. As thread-forming screws tap their own thread during assembly, they do not require the hole to be tapped before insertion.

    Self-Tapping Screw

    Self-Tapping Screws

    Self-tapping screws are commonly used when you need to attach two pieces of material together where you can only access one side of the material. Where you can access both sides, you can use a screw or a bolt. Self-tapping screws are useful when disassembling and reassembling products such as furniture, as they will insert themselves into the same threads they have been removed from.

    Self-Tapping Screws vs Self-Drilling Screws

    Self-tapping and self-drilling screws can easily be confused. Self-tapping screws do not have an integrated drill bit into the screw and certain types of self-tapping screws require a pilot hole to be drilled before they can be driven into the material.

    Self-Drilling Screw

    Self-Drilling Screws

    Self-drilling screws are commonly used in construction, woodworking, and other applications. They differ from self-tapping screws as they drill their own pilot holes and tap threads simultaneously. They have a drill-like point with flutes or cutting edges that remove the material as the screw is driven in. The drill point creates a hole, and then the screw's threads engage the material, providing secure fastening. These screws are ideal for hard materials such as steel, aluminium, or metal alloys.

    Self-Tapping Screws

    Both blunt-nose and flat-ended self-tapping screws require a pilot hole slightly smaller than the screw diameter to be created before they can be driven into the material with a screwdriver. Pointed-nose self-tapping screws do not require pilot holes. The action of driving the screw in will result in the self-tapping screw cutting a thread into the material and securing the materials together. Self-tapping screws secure wood, plastic, metal and brick together.

    There are two types of self-tapping screws - thread-forming and thread-cutting.

    • Thread-Forming: Before you can use these screws you will need to drill a pilot hole as the screw itself does not contain a pointed tip. Thread-forming screws join plastic materials together. Due to their design, they grip materials more tightly. Care should be taken as there is a risk of over-tightening the screw, which can result in the joined materials breaking from the pressure
    • Thread-Tapping: These screws do not require a pilot hole but one can be drilled to make fastening easier. Remember to make the pilot hole smaller than the thread-tapping screw diameter. Thread-tapping screws remove material and create a path for the screw. The drawback to using this type of screw is that when they are removed it can result in stripped threads. If you experience stripped threads, you should use a larger thread-tapping screw when reattachment is made

    If you require Tek screws for wood applications you can use ones manufactured for roofing. The flute on these screws is very small and the diameter of the hole it drills is smaller than the diameter of the outside screw thread. This design allows the screw to bite into the material for a secure hold.

    Anatomy of a Self-Drilling Screw

    *Please note that wings are only present on Remer Tek screws.

    Anatomy of a Self-Drilling Screw Diagram

    Self-Drilling Screw RPM and Force Guide


    Screw Size

    Major Diameter (in.)

    RPM

    Applied Force (lb.)

    Work Material Hardness

    #6

    0.138

    2,200

    80

    20 Rockwell "C" -scale

    #8

    0.164

    1,900

    93

    20 Rockwell "C" -scale

    #10

    0.190

    1,600

    104

    20 Rockwell "C" -scale

    #12

    0.216

    1,400

    116

    20 Rockwell "C" -scale

    #14

    0.250

    1,200

    131

    20 Rockwell "C" -scale

    #16

    0.313

    1,000

    157

    20 Rockwell "C" -scale

    Self-Drilling Screw Troubleshooting Guide

    Self-Drilling Screw Flutes Chipped

    Failure type: Flutes chipped

    Cause of failure: Too much force was used when driving the screw in

    Self-Drilling Screw Melted Flute

    Failure type: Flute melted

    Cause of failure: Too many RPMs used or the material was too hard which resulted in the flute melting

    Self-Drilling Screw with Melted Point

    Failure type: Melted point

    Cause of failure: Material too hard or too much force has been applied

    Self-Drilling Screw Bit Split

    Failure type: Drill bit split

    Cause of failure: Too much force was used when driving the screw in

    No Drilled Hole Self-Drilling Screw

    Failure type: No drilled hole

    Cause of failure: Multiple reasons for failure include too hard material, the driver set to reverse, or the drill point is blunt which could be due to handling or a manufacturer defect

    What Should You Consider When Deciding Which Self-Tapping Screw to Use?

    Self-drilling screws are available in the same head and drive types as self-tapping screws. You should select your screw type based on the material and finish you require. Below we have outlined some factors to consider when selecting.

    • Flute Length – The length of the flute determines the thickness of the metal that a self-drilling screw can be used on. The flute is designed to extract the drilled material from the hole. Cutting will cease if the flute becomes blocked. Simply put, if you attach thick pieces of material, you will need a self-drilling screw with a flute to match. If the flute becomes blocked and you take no action the drill point will likely overheat and fail
    • Drill Point – The drill point refers to the unthreaded section of the screw. When selecting the screw length, you should account for the length of material you are drilling through. If the threads engage before the drill point length is completely through the material it will result in the screw breaking
    • Winged and Non-Winged – It is necessary to use self-drilling screws with wings when fastening wood over 0.5 inches thick to metal. The wings will ream a clearance hold and keep the threads from engaging too early. When the wings engage with the metal they will break off, allowing the threads to engage in the metal. If the threads engage too early this will separate the two materials

    Self-drilling screws are susceptible to the same forces as drill bits. Cutting performance is impacted by the speed and depth of the cut. Make sure to select the correct size screw for your application. This will avoid the drill head melting if too much RPM is applied or snapping if too much pressure is applied. A simple rule of thumb is that small diameter screws can take higher RPM but less force can be used. Transversely, the larger the diameter the lower the RPM, but higher force can be applied.

    Popular Types of Self-Tapping Screws

    Countersunk Self-Tapping Screw

    Countersunk or Flat Head Self-Tapping Screws

    Allows for a flush finish as the screw head sits below the surrounding material. This allows for a flat finish and smooth result.

    Socket Head Self-Tapping Screw

    Allen or Socket Head Self-Tapping Screws

    Less prone to the screw head being compromised and distorted when driven into the material, due to the shape of the driver used.

    Bugle Head Self-Tapping Screw

    Bugle Head Self-Tapping Screws

    The bugle head screw features a countersunk head with a flat top and a concave bearing face. The shape of the bugle head allows the distribution of stress over a much wider area than a flat-head screw.

    Bugle-headed screws attach plasterboard to wood or metal studs.

    Button Head Self-Tapping Screw

    Button and Dome Head Self-Tapping Screws

    They are typically used in carpentry. Due to the dome shape, there is less chance of screw heads countersinking into the material.

    Flange Head Self-Tapping Screw

    Flange Head Self-Tapping Screws

    Usually used to attach metal to metal or plastic to plastic. The flanged head allows more clamping torque than other head types.

    Hex Head Self-Tapping Screw

    Hex Head Self-Tapping Screws

    These screws feature a hexagonal head and are typically used by contractors in heavy-duty applications where a countersunk head is unnecessary.

    Wafer Head Self-Tapping Screw

    Wafer Head Self-Tapping Screws

    Wafer head screws feature a flat top surface and countersunk head. The conical under-head does not extend to the outer edge of the screw head, which allows for a flush fit on wood and other soft materials.

    Pan Head Self-Tapping Screw

    Pan Head Self-Tapping Screws

    The screw head is rounded on the top and vertical on the sides. They are similar to oval or round screws and are typically used in high-torque applications in metal or wood.

    Pancake Head Self-Tapping Screw

    Pancake Head Self-Tapping Screws

    This screw head is used where a large clamping area and an unobstructed head are required. The large clamping area allows force to be distributed across a wider area.

    Square Head Self-Tapping Screw

    Square Head Self-Tapping Screws

    Less susceptible to the bit slipping (cam-out) than a traditional Phillips screw when driving the screw into the material. Care should be taken to ensure that the screw is not over-tightened.

    Truss Head Self-Tapping Screw

    Truss Head Self-Tapping Screws

    This self-tapping screw head is extra wide and has a slightly rounded top, as well as a wider surface area under the screw head. Truss head screws are suitable for sheet metal and other materials with large diameter holes. Their low-dome-shaped head makes tampering with or removing the head difficult.

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    Common Project Questions

    Self-Tapping Screws for Aluminium

    Aluminium has many positive characteristics that make it easy to work with. When using self-tapping screws on aluminium, choose a self-tapping screw with a drill-like point and sharp cutting blade threads that extend down the whole length of the screw. These self-tapping screws are designed to keep thin metal from denting.

    To use self-tapping screws, place the screw directly on the aluminium sheet. The screw's sharp point will make its own hole. Stabilise the screw so it doesn't tilt as it is put in. Let the screw turn until it goes through. Take care not to over-tighten the screw as this can damage the metal or break the screw.

    The advantage of self-tapping screws for aluminium is that they don't need pre-drilling and are easily removed without damaging the metal. They can also be reused in the same material.

    Aluminium in certain applications can vibrate which causes other fastener types to work loose. For example, aluminium is used to build boats. Boat engines cause the boat frame to vibrate which can result in other fasteners such as nails or regular screws falling out. Trilobular stainless steel self-tapping screws are ideal in situations where vibration is present as their thread design reduces friction during thread forming whilst providing resistance to vibrational loosening.

    Self-Tapping Screws for Plastic

    Plastics are more ridged than wood and more prone to cracking. When using self-tapping screws in plastic it is advised that you drill a pilot hole before screwing in the self-tapping screw. If you are installing hardware such as hinges on plastic you will want to avoid drilling the pilot hole fully through the material for aesthetic reasons.

    UPVC Window Screws

    UPVC window screws are available in a variety of lengths but typically come in one diameter (4.8mm gauge). Standard UPVC hardware screws are between 3.9mm and 4.3mm thick. To ensure a tight fit when reattaching window furniture, extra thickness is added to UPVC screws to ensure a secure fit and material for the screw to bite into.

    Self-Tapping Screws for Fibreglass

    Fibreglass consists of glass fibres embedded in resin. The combination of glass fibres and resin makes for a very strong material. When using self-tapping screws in fibreglass, you will find that the drilling tip of the screw becomes dull quickly as it comes into contact with the glass fibres, which leads to cracking in the glass fibres and the gel coat. To avoid cracking, proper installation techniques must be used.

    FAQs

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