Complete metric and imperial thread reference — tap drill sizes, pitch, and clearance holes
| Thread Size | Thread Pitch (mm/TPI) | Tap Drill Size | Clearance Hole | Drill Size (mm/in) |
|---|
Quick reference for tapping holes. For metric threads, tap drill = major dia - pitch. For imperial, follow standard chart. Use 75% thread engagement for most applications.
— Vaibhav Dhokpande, Developer · TaskJunction
A drill and tap size chart tells you which drill to use before tapping a thread. The tap drill creates the minor diameter of the thread — the cutting teeth of the tap form the thread profile from this hole. Using a drill that is too small makes tapping difficult and risks tap breakage. Too large a drill gives insufficient thread engagement.
Standard charts assume 75% thread engagement, which provides 95%+ of the theoretical thread strength while being practical to produce. For through-hole applications in mild steel with standard bolts, 75% is always the right choice.
For blind holes in hard materials (tool steel, stainless), go to 65–70% engagement (slightly larger tap drill) to reduce the chance of breaking an expensive tap. The small reduction in thread strength is almost never the weak link — the bolt will yield before a properly formed 65% thread strips.
| Thread Type | Use When | Example |
|---|---|---|
| Coarse (standard) | General purpose, easy assembly | M10×1.5 |
| Fine | Precision adjustment, thin walls | M10×1.0 |
| Extra Fine | Instrument work, very thin sections | M10×0.75 |
Shop floor tip: Keep coarse thread taps for general work. Fine thread taps are fragile — they snap easily if the drill is even slightly undersize or if the workpiece moves during tapping. Use a tapping stand or tapping head whenever possible, never tap by hand in CNC fixtures.