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Tap Drill Size Chart
Recommended drill sizes for machine screw and fractional taps, at 75% (standard) and 50% (easier tapping in hard materials) thread engagement.
| Tap size | Drill @ 75% | Drill @ 50% |
|---|
Standard: ANSI B94.11M / ISO 724 · Data checked: 2026-10-14
Frequently asked questions
What does 75% thread mean?
It is the percentage of full thread depth actually cut. A 75% thread is the usual recommendation: it gives around 90% of the strength of a 100% thread while needing much less torque, so taps break far less often. Going to 100% buys very little strength for a large increase in risk.
Can I use the same hole for cutting and forming taps?
No. Forming (roll) taps displace material rather than cutting it, so they need a larger starting hole — roughly the pitch diameter of the thread minus half the pitch. Using a cutting tap's drill size with a forming tap will break the tap.
Why are there two columns, 75% and 50%?
The 50% column is for thin material, hard-to-tap materials, or where the fastener's full strength is not needed. It is easier to tap and less likely to break a tap, at the cost of a weaker thread.
Does the chart cover metric threads?
The tap drill chart lists inch sizes (UNC and UNF). For metric, the rule is nominal diameter minus pitch — the metric bolt size calculator on this site gives the tap drill for every size from M3 to M36.