Mechanism and Features of Self-tapping Screws - Self-tapping screws have various tip and thread patterns. - Common features include a screw thread covering the entire length of the screw and a hardened thread for the intended substrate. - For hard substrates like metal or hard plastics, a gap is cut in the thread to create a flute and cutting edge, allowing the screw to tap its own hole. - For softer substrates like wood or soft plastics, a tapered tip is used to displace the surrounding material and form a hole. - Some self-tapping screws have a blunt tip (type B) for use with a pilot hole, making handling and packaging easier.

Thread-forming vs. Thread-cutting Self-tapping Screws - Thread-forming self-tapping screws displace material without removing it. - Thread-cutting self-tapping screws have sharp cutting surfaces that remove the material as they are inserted. - Thread-forming screws may have non-circular plan views like pentalobular or Taptite screws. - Thread-cutting screws may have flutes machined into their threads, providing cutting edges.

Self-drilling Screws - Some self-tapping screws, like the Tek screw brand, are also self-drilling. - Self-drilling screws combine hole drilling, threading, and fastener installation into one motion. - They are efficient for hard-substrate applications, from assembly lines to roofing. - Some types of self-drilling screws incorporate a sealing washer for fastening roofing sheets to purlins.

Sheet Metal Screws - Sheet metal screws can form a thread in thin sheet metal. - Pan-head self-tapping screws are common in metal cases for electrical equipment. - Flatter-headed truss or flat countersunk headed self-tapping screws are found in aviation applications.

Winged Self-tapper - Winged self-drilling screws have thin wings wider than the thread formed just behind the self-drilling head. - These screws cut a clearance hole in soft materials but are destroyed by more robust materials. - They allow for a single operation to clamp material to metal, including clearance drilling, tap drilling, thread tapping, and fixing.