Self-tapping screw

A self-tapping screw is a screw that can tap its own threads as it is driven into a pre-drilled hole, eliminating the need for a separate tapping operation. The thread-cutting feature — either a sharp, hardened point or a drill-shaped tip — cuts or forms threads in the material as the screw advances.

How it works

The screw is driven into a pilot hole (a hole drilled slightly smaller than the screw’s major diameter). As the screw advances, its hardened thread either cuts into the material (thread-cutting screws) or displaces it (thread-forming screws), creating its own mating threads. This is faster and cheaper than drilling a hole, tapping it, and then installing a separate bolt.

Types

• Thread-cutting screw: Has a sharpened notch or slot at the tip that cuts threads by removing material. The chips are cleared by the flutes in the notch. Used in metal, plastic, and cast iron.
• Thread-forming screw (Taptite): Has a slightly reduced, unthreaded shank that forms threads by displacing material rather than cutting it. The displaced material cold-flows around the thread, creating a tighter, vibration-resistant joint. Common in sheet metal and automotive assembly.
• Self-drilling screw (TEK screw): Has a drill-bit tip that drills its own pilot hole and taps its own threads in a single operation. No pre-drilling required. Common in metal roofing, HVAC, and steel framing.

When to use them

Self-tapping screws are ideal for high-volume assembly where speed matters — sheet metal fabrication, HVAC ductwork, electronics enclosures, and automotive trim. They are less suitable for applications requiring frequent disassembly, as the threads they create are typically less precise than those made by a proper tap.