3/4-10 Tap Drill Size & Thread Specs
Everything for a 3/4-10 UNC thread on one page: tap drill (21/32), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · 3/4-10
3/4-10 specs
SizePlate
3/4-10 UNC · tap with
21/32 drill
.6563″
16.67 mm · 72% thread
- Metric drill
- 16.5 mm · .6496
- Clearance
- 49/64 / 25/32
- Wrench
- 1-1/8″
- Cap screw key
- 5/8″
Thread
- Nominal size
- 3/4″ · 19.05 mm
- Major diameter
- .7500″
- Threads per inch
- 10
- Pitch
- .1000″ · 2.540 mm
- Series
- UNC (coarse)
- UNF version
- 3/4-16
Drilling
- Tap drill (75%)
- 21/32 · .6563
- Metric substitute
- 16.5 mm · .6496
- Tap drill (≈50%)
- 11/16 · .6875
- Close fit
- 49/64 · .7656
- Free fit
- 25/32 · .7813
Tools
- Hex bolt wrench
- 1-1/8″
- Hex nut wrench
- 1-1/8″
- Socket head cap key
- 5/8″
- Button head key
- —
- Flat head key
- 1/2″
Nearest metric
- Thread
- M20 × 2.5
- Major diameter
- 20 mm
- Pitch
- 2.5 mm
- Tap drill
- 17.5 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 |
|---|---|---|---|
| 41/64 | .6406 | 16.27 | 84% |
| 16.5 mm | .6496 | 16.5 | 77% |
| 21/32 | .6563 | 16.67 | 72% |
| 17 mm | .6693 | 17 | 62% |
| 43/64 | .6719 | 17.07 | 60% |
| 11/16 | .6875 | 17.46 | 48% |
| 17.5 mm | .6890 | 17.5 | 47% |
Neighboring sizes
Questions
What does 3/4-10 mean?
A 3/4″ nominal diameter with 10 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is 3/4-16.
Can I use a 16.5 mm drill instead of 21/32?
Usually. 16.5 mm is .6496″ against .6563″ for 21/32, 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.