9/16-12 Tap Drill Size & Thread Specs

Everything for a 9/16-12 UNC thread on one page: tap drill (31/64), clearance holes, wrench and hex key sizes, and the nearest metric thread.

SP-TD-01 · 9/16-12

9/16-12 specs

SizePlate

9/16-12 UNC · tap with

31/64 drill

.4844″

12.3 mm · 72% thread

Metric drill: 12.3 mm · .4843
Clearance: 37/64 / 19/32
Wrench: 13/16″

Thread

Nominal size: 9/16″ · 14.29 mm
Major diameter: .5625″
Threads per inch: 12
Pitch: .0833″ · 2.117 mm
Series: UNC (coarse)
UNF version: 9/16-18

Drilling

Tap drill (75%): 31/64 · .4844
Metric substitute: 12.3 mm · .4843
Tap drill (≈50%): 33/64 · .5156
Close fit: 37/64 · .5781
Free fit: 19/32 · .5938

Tools

Hex bolt wrench: 13/16″
Hex nut wrench: 7/8″
Socket head cap key: —
Button head key: —
Flat head key: —

Nearest metric

Thread: M14 × 2.0
Major diameter: 14 mm
Pitch: 2 mm
Tap drill: 12 mm
Interchangeable: No

Not interchangeable means the threads look close but won't run together: forcing one into the other strips both.

Drill size by thread percentage

Larger drill, less thread, easier tapping. 75% is the usual target.

Drill	Decimal	mm	Thread
12 mm	.4724	12	83%
12.1 mm	.4764	12.1	80%
12.2 mm	.4803	12.2	76%
12.3 mm	.4843	12.3	72%
31/64	.4844	12.3	72%
12.4 mm	.4882	12.4	69%
12.5 mm	.4921	12.5	65%
12.6 mm	.4961	12.6	61%
1/2	.5000	12.7	58%
12.7 mm	.5000	12.7	58%
12.8 mm	.5039	12.8	54%
12.9 mm	.5079	12.9	50%
13 mm	.5118	13	47%

Neighboring sizes

Questions

What does 9/16-12 mean?

A 9/16″ nominal diameter with 12 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is 9/16-18.

Can I use a 12.3 mm drill instead of 31/64?

Usually. 12.3 mm is .4843″ against .4844″ for 31/64, which changes the thread engagement by a few percent at most. The thread-percentage table above shows exactly how much thread each nearby drill leaves.