O Drill Size

letter drill

O 0.316 in 8.03 mm

A O drill measures 0.316 in. It taps 1 thread in this chart.

What a O 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 O drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
3/8-16	72.7%	5/16″	77.0%

Drills either side

M 0.295 in · 7.49 mm Next size down
P 0.323 in · 8.2 mm Next size up

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

O drill: common questions

What size is a O drill?

0.316 inches, which is 8.03 mm. It is a letter drill.

What can I tap with a O drill?

1 thread: 3/8-16 at 72.7%.

What drill is next to a O?

Down: M at 0.295 in. Up: P at 0.323 in.