Self-Tapping vs Self-Drilling vs Thread-Forming Screws: The Complete Guide

Even experienced engineers get confused by these terms. The fastener industry uses "self-tapping" and "self-drilling" almost interchangeably, and "thread-forming" gets thrown around without clear definitions. Let us clear this up once and for all.

The Quick Answer

• Self-Drilling = Has a drill-bit point, makes its own hole, NO pilot hole needed
• Self-Tapping = Umbrella term for screws that create their own threads (includes thread-forming AND thread-cutting)
• Thread-Forming = A type of self-tapping that displaces material (no chips)
• Thread-Cutting = A type of self-tapping that cuts material (creates chips)

Self-Drilling Screws (TEK Screws)

Self-drilling screws have an actual drill-bit point that bores its own hole through the material. No pilot hole required — the screw does all the work.

Key Characteristics:

• Drill-bit tip that penetrates material
• Primarily for metal-to-metal applications
• Also called TEK screws or drill-point screws
• Saves time by eliminating the pre-drilling step

Point Types (Drill Capacity):

Higher point numbers = longer drill flute = thicker material capacity

Self-Tapping Screws (The Umbrella Term)

Here is where the confusion starts. Self-tapping is a broad category that includes any screw that creates its own mating threads. This includes both thread-forming and thread-cutting screws.

Unlike self-drilling screws, self-tapping screws require a pilot hole — they tap the threads, but they do not drill the initial hole.

Thread-Forming Screws

Thread-forming screws displace material to create threads without removing any metal. Think of it like pushing material aside rather than cutting it away.

Best for: Sheet metal, soft metals, plastics, plywood

Common Point Types:

• Type A — Coarse threads, gimlet point, for sheet metal up to 0.050\"
• Type AB — Finer threads than Type A, gimlet point, for sheet metal and resinous plywood
• Type B — Finer pitch, blunt point, for sheet metal 0.050\" and thicker
• Type C — Machine screw thread pitch, blunt point, for applications requiring interchangeability with machine screws

Thread-Cutting Screws

Thread-cutting screws have cutting edges that remove material, creating chips as they form threads. They work like a tap.

Best for: Harder materials, castings, brittle plastics, die castings

Common Point Types:

• Type 1 — Blunt point with tapered threads and cutting slot
• Type 17 — Similar to Type 1 but with a longer point for wood applications
• Type 23 — Machine screw thread, for plastics and metals
• Type 25 — Coarse thread for brittle plastics and die castings
• Type F — Machine screw thread, multi-cutting edge, for heavy-gauge sheet metal
• Type T — Similar to Type 23, for plastics
• Type BF — Combines Type B body with Type F cutting threads
• Type BT — Combines Type B body with Type T cutting threads

How to Choose the Right Screw

Choose Self-Drilling (TEK) When:

• You are fastening metal to metal
• You want to eliminate pre-drilling
• Speed and efficiency are priorities
• Material thickness matches the point type capacity

Choose Thread-Forming When:

• Working with sheet metal, plastics, or soft materials
• You can pre-drill a pilot hole
• You need strong thread engagement
• Chips and debris are a concern

Choose Thread-Cutting When:

• Material is too hard for thread-forming
• Working with castings or brittle materials
• You need precise thread fit
• The material cannot tolerate deformation

Quick Reference Chart

Need Help Selecting the Right Fastener?

Our team at ECOM Fasteners has decades of experience helping engineers, contractors, and DIYers find the exact fastener for their application. Contact us for expert guidance, or browse our selection:

• Self-Drilling Screws (TEK Screws)
• Sheet Metal Screws
• Machine Screws

Same quality as McMaster-Carr, better prices on quantity.