#51 Drill Size

number drill

#51 0.067 in 1.70 mm

A #51 drill measures 0.067 in. It taps 2 threads in this chart.

What a #51 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 #51 drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
#2-56	81.9%	#50	69.0%
M2 x 0.4	57.4%	1.6 mm	77.0%

Other jobs for a #51

Form-tap hole: The published roll-tap hole for #1-64, #1-72. A form tap displaces metal instead of cutting it, so it needs this larger hole.
Clearance hole: The through hole a bolt passes in, not a tapped hole: close fit for #0-80. See the clearance hole chart.

Drills either side

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

#51 drill: common questions

What size is a #51 drill?

0.067 inches, which is 1.70 mm. It is a number drill.

What can I tap with a #51 drill?

2 threads: #2-56 at 81.9%, M2 x 0.4 at 57.4%.

Is a #51 drill used for clearance holes?

Yes: close fit for #0-80. A clearance hole is not tapped; the bolt passes through it.

What drill is next to a #51?

Down: 1.7 mm at 0.0669 in. Up: 1.75 mm at 0.0689 in.