T Drill Size

letter drill

T 0.358 in 9.09 mm

A T drill measures 0.358 in. It taps 2 threads in this chart.

What a T 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 T drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M10 x 1	69.8%	9 mm	77.0%
M10 x 1.25	55.9%	8.8 mm	73.9%

Other jobs for a T

Form-tap hole: The published roll-tap hole for 3/8-24. A form tap displaces metal instead of cutting it, so it needs this larger hole.

Drills either side

9 mm 0.3543 in · 9 mm Next size down
9.1 mm 0.3583 in · 9.1 mm Next size up

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

T drill: common questions

What size is a T drill?

0.358 inches, which is 9.09 mm. It is a letter drill.

What can I tap with a T drill?

2 threads: M10 x 1 at 69.8%, M10 x 1.25 at 55.9%.

What drill is next to a T?

Down: 9 mm at 0.3543 in. Up: 9.1 mm at 0.3583 in.