I Drill Size

letter drill

I 0.272 in 6.91 mm

A I drill is the standard tap drill for 5/16-24.

What a I 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 I drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M8 x 1	84.0%	7 mm	77.0%
5/16-24 chart drill	74.8%	I	74.8%
M8 x 1.25	67.2%	6.8 mm	73.9%
5/16-18	56.1%	F	76.9%

Other jobs for a I

Hard-material tap drill: The size to use in stainless or tool steel for 5/16-18, where it leaves a shallower thread than the standard drill and cuts tapping torque.

Drills either side

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

I drill: common questions

What size is a I drill?

0.272 inches, which is 6.91 mm. It is a letter drill.

What can I tap with a I drill?

4 threads: M8 x 1 at 84.0%, 5/16-24 at 74.8%, M8 x 1.25 at 67.2%, 5/16-18 at 56.1%.

Is a I drill the standard tap drill for anything?

Yes, for 5/16-24 (74.8% thread). That is the size published tap and drill charts give.

What drill is next to a I?

Down: 6.9 mm at 0.2717 in. Up: 7 mm at 0.2756 in.