Tap Drill Size Chart
Pilot hole size for any tap thread
📚 Learn more — how it works, FAQ & guide Click to expand
Learn more — how it works, FAQ & guide
Click to expand
Tap drill size calculator
Find the correct drill bit for any tap. UNC, UNF, metric.
How to use this tool
- 1
Pick tap size
Select from standard UNC/UNF/metric.
- 2
Pick thread engagement %
75% standard; 50% for hard materials.
- 3
See drill size
Exact + closest standard bit.
Frequently Asked Questions
Why 75% thread engagement?
Standard engagement. Gives 95% of thread strength but 66% of the drilling effort vs 100%. Industry default for most jobs.
When to use 50%?
Hardened steels, stainless, or when breaking taps is a concern. Weaker threads but much easier tapping.
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