3/4-16 Tap Drill Size & Thread Specs
Everything for a 3/4-16 UNF thread on one page: tap drill (11/16), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · 3/4-16
3/4-16 specs
SizePlate
3/4-16 UNF · tap with
11/16 drill
.6875″
17.46 mm · 77% thread
- Metric drill
- 17.5 mm · .6890
- 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
- 16
- Pitch
- .0625″ · 1.587 mm
- Series
- UNF (fine)
- UNC version
- 3/4-10
Drilling
- Tap drill (75%)
- 11/16 · .6875
- Metric substitute
- 17.5 mm · .6890
- Tap drill (≈50%)
- 45/64 · .7031
- 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 |
|---|---|---|---|
| 11/16 | .6875 | 17.46 | 77% |
| 17.5 mm | .6890 | 17.5 | 75% |
| 45/64 | .7031 | 17.86 | 58% |
| 18 mm | .7087 | 18 | 51% |
Neighboring sizes
Questions
What does 3/4-16 mean?
A 3/4″ nominal diameter with 16 threads per inch. It’s the fine (UNF) thread for that size; the coarse version is 3/4-10.
Can I use a 17.5 mm drill instead of 11/16?
Usually. 17.5 mm is .6890″ against .6875″ for 11/16, 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.