1/2-20 Tap Drill Size & Thread Specs
Everything for a 1/2-20 UNF thread on one page: tap drill (29/64), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · 1/2-20
1/2-20 specs
SizePlate
1/2-20 UNF · tap with
29/64 drill
.4531″
11.51 mm · 72% thread
- Metric drill
- 11.5 mm · .4528
- 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
- 20
- Pitch
- .0500″ · 1.270 mm
- Series
- UNF (fine)
- UNC version
- 1/2-13
Drilling
- Tap drill (75%)
- 29/64 · .4531
- Metric substitute
- 11.5 mm · .4528
- Tap drill (≈50%)
- 15/32 · .4688
- 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 |
|---|---|---|---|
| 11.3 mm | .4449 | 11.3 | 85% |
| 11.4 mm | .4488 | 11.4 | 79% |
| 11.5 mm | .4528 | 11.5 | 73% |
| 29/64 | .4531 | 11.51 | 72% |
| 11.6 mm | .4567 | 11.6 | 67% |
| 11.7 mm | .4606 | 11.7 | 61% |
| 11.8 mm | .4646 | 11.8 | 55% |
| 11.9 mm | .4685 | 11.9 | 48% |
| 15/32 | .4688 | 11.91 | 48% |
Neighboring sizes
Questions
What does 1/2-20 mean?
A 1/2″ nominal diameter with 20 threads per inch. It’s the fine (UNF) thread for that size; the coarse version is 1/2-13.
Can I use a 11.5 mm drill instead of 29/64?
Usually. 11.5 mm is .4528″ against .4531″ for 29/64, 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.