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Tapping screws

Tapping screws are fasteners that form or cut a internal thread in the mating material as they are driven in, requiring no nut or prior tapping. Drill screws (Tek screws), which have a drill-shaped cutting tip at the point, can drill the pilot hole, form the thread, and fasten in a single operation. Head styles include pan, countersunk, truss, and hexagonal; countersunk heads are used when a flush finish is required. For fixing wood wool boards or wood-based boards to steel substrates, types with wings (fins) that prevent the upper panel from lifting together with the screw, and full-thread or half-thread versions are selected according to use. Materials include steel and corrosion-resistant stainless steel (such as SUS410), used for structural steel fastening at construction sites and outdoor fixing.

How to choose Tapping screws

  1. 1. Select the range that matches the steel substrate thickness

    Drill screws have both an upper and lower limit on the steel sheet thickness they can drill through with the cutting tip. The listed products have a lower limit of 1.6 mm and an upper limit of 2.3 to 3.2 mm. If the substrate is thicker than the range, the cutting tip wears before the hole is drilled; if thinner, the thread engagement is insufficient. Check both the upper and lower limits against the plate thickness of the substrate steel.

  2. 2. Determine the length from the total fastening thickness

    The overall length is determined by the combined thickness of the upper panel and substrate, plus the length needed for the cutting section to fully penetrate. The listed products range from 28 to 100 mm, and the upper and lower fastening thickness limits are specified for each product. If the thread engages before the cutting section (7 to 7.5 mm long) passes through the substrate, the screw may break, so confirm within the fastening thickness range.

  3. 3. Choose between full-thread and half-thread types

    Half-thread screws have a plain cylindrical section under the head, so they can pull the upper panel down to the substrate without being pushed up by the threads, which suits fixing thick boards. In the listed products, the 35 and 45 mm lengths are full-thread and 50 mm and longer are half-thread. Select the type according to the upper panel thickness and fixing method.

  4. 4. Check the thread outer diameter and cutting tip outer diameter

    The thread outer diameter affects holding power and pilot hole diameter. The listed products have outer diameters of 4.2 to 5 mm, and the cutting tip outer diameter is 3.5 to 4.2 mm. The cutting tip outer diameter is smaller than the thread outer diameter and corresponds to the pilot hole for forming the internal thread. Select the nominal size according to the load conditions, the hole diameter in the upper panel, and the dimensions of the mating member.

  5. 5. Match the Phillips drive size and head style

    Using a bit that does not match the Phillips drive number increases cam-out (bit slipping out) and damage to the recess. For a flush finish, select a countersunk head, and confirm that the head outer diameter of 10 to 12 mm fits within the seating surface or board surface. Match the bit number to the bits used on site.

  6. 6. Select material and surface treatment for the service environment

    Steel products with trivalent chromate plating are available for indoor use, and SUS410 products with corrosion-resistant treatment are available for outdoor or corrosive environments. SUS410 is a martensitic grade that gains hardness by quenching, and is used for drill screws. However, its corrosion resistance is inferior to austenitic grades such as SUS304.

This guide was written by AI based on the listed products' documents and specification items. Check each manufacturer's documents before adopting.