Tap Drill Calculator
Cut and roll-form tap drills at any percent of thread — with the nearest standard drills and what each actually gives you.
Results
Nearest standard drills
| Drill | System | Decimal (in) | mm | % thread it gives |
|---|
About the percentage. Standard charts use 75%, which sits comfortably inside the Class 2B minor-diameter
limits of ASME B1.1. Going higher than ~75% adds tapping torque with little strength gain. Going much lower runs
into the spec: for most common inch sizes the 2B maximum minor diameter lands around 66–67% thread, so a 60%
hole is out of tolerance even though the thread may still gauge on pitch diameter. Roll-form taps are figured on a
different scale — their percentages are not comparable to cut-tap percentages, and the formed crest ends up below
the drilled hole size.
Full write-up: Tap Drill Size & Percent of Thread, Explained ·
Cut vs. Roll Form Taps: When and Why.