Tap Drill Size Chart

X Drill Size

letter drill

X 0.397 in 10.08 mm

A X drill measures 0.397 in. It taps 2 threads in this chart.

What a X drill taps

Every thread this drill cuts between 50% and 85% of thread, deepest first. Outside that band it is the wrong drill for the job, so nothing below that line is listed.

Threads a X drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread % thread Chart drill Chart %
M12 x 1.75 84.3% 10.2 mm 79.2%
7/16-20 62.4% 25/64″ 72.2%

Other jobs for a X

Hard-material tap drill
The size to use in stainless or tool steel for 7/16-20, where it leaves a shallower thread than the standard drill and cuts tapping torque.

Drills either side

All drill sizes → · Open this drill in the calculator →

X drill: common questions

What size is a X drill?
0.397 inches, which is 10.08 mm. It is a letter drill.
What can I tap with a X drill?
2 threads: M12 x 1.75 at 84.3%, 7/16-20 at 62.4%.
What drill is next to a X?
Down: 25/64 in at 0.3906 in. Up: 10.1 mm at 0.3976 in.