B Drill Size

letter drill

B 0.238 in 6.05 mm

A B drill measures 0.238 in. It taps 1 thread in this chart.

What a B 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 B drill taps, with the percent of thread each one gets and the published chart drill for comparison.
Thread	% thread	Chart drill	Chart %
M7 x 1	73.5%	6 mm	77.0%

Other jobs for a B

Clearance hole: The through hole a bolt passes in, not a tapped hole: loose fit for #10-24, loose fit for #10-32. See the clearance hole chart.

Drills either side

A 0.234 in · 5.94 mm Next size down
C 0.242 in · 6.15 mm Next size up

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

B drill: common questions

What size is a B drill?

0.238 inches, which is 6.05 mm. It is a letter drill.

What can I tap with a B drill?

1 thread: M7 x 1 at 73.5%.

Is a B drill used for clearance holes?

Yes: loose fit for #10-24, loose fit for #10-32. A clearance hole is not tapped; the bolt passes through it.

What drill is next to a B?

Down: A at 0.234 in. Up: C at 0.242 in.