Fixtra

Tap Drill & Thread Calculator

Pick a thread (or type your own major diameter and pitch) and get the tap drill size for your target percent thread, the clearance drill sizes, and the pitch / TPI. Works in metric and inch.

Thread

Standard size

Major diameter mm

Pitch mm/thread

Inch threads: enter pitch as 1/TPI, or pick a standard size above.

Target thread engagement %

75%

~75% is the common production choice (good strength, reasonable tapping torque). Higher % = stronger but harder to tap and breaks taps.

Results

Tap drill (75% thread)—

Pitch / TPI—

Clearance — close—

Clearance — normal—

Clearance — loose—

Tap drill = major − (%thread ÷ 100 × 1.0825 × pitch). Round to the nearest real drill you have — a touch larger eases tapping, a touch smaller raises strength and torque. Clearance holes are for the bolt to pass through (close/normal/loose fit classes).