1/2-13 Tap Drill Size & Thread Specs
Everything for a 1/2-13 UNC thread on one page: tap drill (27/64), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · 1/2-13
1/2-13 specs
SizePlate
1/2-13 UNC · tap with
27/64 drill
.4219″
10.72 mm · 78% thread
- Metric drill
- 10.7 mm · .4213
- Clearance
- 33/64 / 17/32
- Wrench
- 3/4″
- Cap screw key
- 3/8″
Thread
- Nominal size
- 1/2″ · 12.7 mm
- Major diameter
- .5000″
- Threads per inch
- 13
- Pitch
- .0769″ · 1.954 mm
- Series
- UNC (coarse)
- UNF version
- 1/2-20
Drilling
- Tap drill (75%)
- 27/64 · .4219
- Metric substitute
- 10.7 mm · .4213
- Tap drill (≈50%)
- 29/64 · .4531
- Close fit
- 33/64 · .5156
- Free fit
- 17/32 · .5313
Tools
- Hex bolt wrench
- 3/4″
- Hex nut wrench
- 3/4″
- Socket head cap key
- 3/8″
- Button head key
- 5/16″
- Flat head key
- 5/16″
Nearest metric
- Thread
- M12 × 1.75
- Major diameter
- 12 mm
- Pitch
- 1.75 mm
- Tap drill
- 10.2 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 |
|---|---|---|---|
| 10.6 mm | .4173 | 10.6 | 83% |
| 10.7 mm | .4213 | 10.7 | 79% |
| 27/64 | .4219 | 10.72 | 78% |
| 10.8 mm | .4252 | 10.8 | 75% |
| 10.9 mm | .4291 | 10.9 | 71% |
| 11 mm | .4331 | 11 | 67% |
| 11.1 mm | .4370 | 11.1 | 63% |
| 7/16 | .4375 | 11.11 | 63% |
| 11.2 mm | .4409 | 11.2 | 59% |
| 11.3 mm | .4449 | 11.3 | 55% |
| 11.4 mm | .4488 | 11.4 | 51% |
| 11.5 mm | .4528 | 11.5 | 47% |
| 29/64 | .4531 | 11.51 | 47% |
Neighboring sizes
Questions
What does 1/2-13 mean?
A 1/2″ nominal diameter with 13 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is 1/2-20.
Can I use a 10.7 mm drill instead of 27/64?
Usually. 10.7 mm is .4213″ against .4219″ for 27/64, 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.