Selftapping

Self-tapping refers to fasteners that create their own mating threads in a material as they are installed, eliminating the need for a separate tapping operation. Self-tapping screws fall into two main categories based on how they interact with the substrate: thread-cutting screws, which cut and form threads in the material, and thread-forming screws, which displace material to form the threads without removing it. A subset known as self-drilling screws has a drill-like tip that can bore a pilot hole as it penetrates, often allowing installation without pre-drilling in metal applications.

These fasteners are widely used in wood, metal, plastic, and composite assemblies. In wood, self-tapping screws typically have sharp points to begin thread formation in softer substrates and may or may not require a pilot hole. In metal and sheet metal, pilot holes are common, though self-drilling variants can eliminate this step. In plastics, screws are designed to cut or form threads without fracturing the material. Materials for the screws include carbon steel and stainless steel, often with coatings such as zinc plating or galvanization for corrosion resistance.

Advantages of self-tapping screws include faster assembly, reduced need for pre-tap operations, and suitability for joining thin or soft materials. Limitations include the need for appropriate material ductility and hole preparation, potential for thread stripping under high loads or vibration, and the necessity of selecting the correct length and thread type for the material and joint. For high-load or thick substrates, alternatives such as nuts, inserts, or through-bolts may be used in conjunction with or instead of self-tapping fasteners.