21 mm Drill Size

metric drill

21 mm 0.8268 in 21.00 mm

A 21 mm drill is the standard tap drill for M24 x 3.

What a 21 mm 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 21 mm drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M24 x 3 chart drill	77.0%	21 mm	77.0%
7/8-20	74.2%	53/64″	72.2%
7/8-14	51.9%	13/16″	67.4%
M22 x 1.5	51.3%	20.5 mm	77.0%

Other jobs for a 21 mm

Hard-material tap drill: The size to use in stainless or tool steel for M22 x 1.5, where it leaves a shallower thread than the standard drill and cuts tapping torque.
Form-tap hole: The published roll-tap hole for M22 x 2.5, M22 x 2. A form tap displaces metal instead of cutting it, so it needs this larger hole.

Drills either side

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21 mm drill: common questions

What size is a 21 mm drill?

0.8268 inches, which is 21.00 mm. It is a metric drill.

What can I tap with a 21 mm drill?

4 threads: M24 x 3 at 77.0%, 7/8-20 at 74.2%, 7/8-14 at 51.9%, M22 x 1.5 at 51.3%.

Is a 21 mm drill the standard tap drill for anything?

Yes, for M24 x 3 (77.0% thread). That is the size published tap and drill charts give.

What drill is next to a 21 mm?

Down: 13/16 in at 0.8125 in. Up: 53/64 in at 0.8281 in.