Q Drill Size

letter drill

Q 0.332 in 8.43 mm

A Q drill is the standard tap drill for 3/8-24.

What a Q 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 Q drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M10 x 1.5	80.4%	8.5 mm	77.0%
3/8-24 chart drill	79.4%	Q	79.4%
3/8-16	53.0%	5/16″	77.0%

Drills either side

8.4 mm 0.3307 in · 8.4 mm Next size down
8.5 mm 0.3346 in · 8.5 mm Next size up

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

Q drill: common questions

What size is a Q drill?

0.332 inches, which is 8.43 mm. It is a letter drill.

What can I tap with a Q drill?

3 threads: M10 x 1.5 at 80.4%, 3/8-24 at 79.4%, 3/8-16 at 53.0%.

Is a Q drill the standard tap drill for anything?

Yes, for 3/8-24 (79.4% thread). That is the size published tap and drill charts give.

What drill is next to a Q?

Down: 8.4 mm at 0.3307 in. Up: 8.5 mm at 0.3346 in.