45/64 in Drill Size

fractional drill

45/64″ 0.7031 in 17.86 mm

A 45/64 in drill is the standard tap drill for 3/4-20.

What a 45/64 in 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 45/64 in drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M20 x 2	82.4%	18 mm	77.0%
3/4-20 chart drill	72.2%	45/64″	72.2%
M20 x 2.5	65.9%	17.5 mm	77.0%
3/4-16	57.8%	11/16″	77.0%

Other jobs for a 45/64 in

Hard-material tap drill: The size to use in stainless or tool steel for 3/4-16, where it leaves a shallower thread than the standard drill and cuts tapping torque.
Form-tap hole: The published roll-tap hole for 3/4-10. A form tap displaces metal instead of cutting it, so it needs this larger hole.

Drills either side

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45/64 in drill: common questions

What size is a 45/64 in drill?

0.7031 inches, which is 17.86 mm. It is a fractional drill.

What can I tap with a 45/64 in drill?

4 threads: M20 x 2 at 82.4%, 3/4-20 at 72.2%, M20 x 2.5 at 65.9%, 3/4-16 at 57.8%.

Is a 45/64 in drill the standard tap drill for anything?

Yes, for 3/4-20 (72.2% thread). That is the size published tap and drill charts give.

What drill is next to a 45/64 in?

Down: 17.8 mm at 0.7008 in. Up: 17.9 mm at 0.7047 in.