#18 Drill Size

number drill

#18 0.1695 in 4.31 mm

A #18 drill measures 0.1695 in. It taps 2 threads in this chart.

What a #18 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 #18 drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M5 x 0.8	66.9%	4.2 mm	77.0%
#10-32	50.5%	#21	76.4%

Other jobs for a #18

Clearance hole: The through hole a bolt passes in, not a tapped hole: normal fit for #6-32, normal fit for #6-40. See the clearance hole chart.

Drills either side

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#18 drill: common questions

What size is a #18 drill?

0.1695 inches, which is 4.31 mm. It is a number drill.

What can I tap with a #18 drill?

2 threads: M5 x 0.8 at 66.9%, #10-32 at 50.5%.

Is a #18 drill used for clearance holes?

Yes: normal fit for #6-32, normal fit for #6-40. A clearance hole is not tapped; the bolt passes through it.

What drill is next to a #18?

Down: 4.3 mm at 0.1693 in. Up: 11/64 in at 0.1719 in.