#10-32 Tap Drill Size & Thread Specs
Everything for a #10-32 UNF thread on one page: tap drill (#21), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #10-32
#10-32 specs
SizePlate
#10-32 UNF · tap with
#21 drill
.1590″
4.04 mm · 76% thread
- Metric drill
- 4 mm · .1575
- Clearance
- #9 / #7
- Wrench
- 3/8″
- Cap screw key
- 5/32″
Thread
- Nominal size
- #10 · 4.83 mm
- Major diameter
- .1900″
- Threads per inch
- 32
- Pitch
- .0312″ · 0.794 mm
- Series
- UNF (fine)
- UNC version
- #10-24
Drilling
- Tap drill (75%)
- #21 · .1590
- Metric substitute
- 4 mm · .1575
- Tap drill (≈50%)
- #18 · .1695
- Close fit
- #9 · .1960
- Free fit
- #7 · .2010
Tools
- Hex bolt wrench
- —
- Hex nut wrench
- 3/8″
- Socket head cap key
- 5/32″
- Button head key
- 1/8″
- Flat head key
- 1/8″
Nearest metric
- Thread
- M5 × 0.8
- Major diameter
- 5 mm
- Pitch
- 0.8 mm
- Tap drill
- 4.2 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 |
|---|---|---|---|
| 5/32 | .1563 | 3.97 | 83% |
| #22 | .1570 | 3.99 | 81% |
| 4 mm | .1575 | 4 | 80% |
| #21 | .1590 | 4.04 | 76% |
| #20 | .1610 | 4.09 | 71% |
| 4.1 mm | .1614 | 4.1 | 70% |
| 4.2 mm | .1654 | 4.2 | 61% |
| #19 | .1660 | 4.22 | 59% |
| 4.3 mm | .1693 | 4.3 | 51% |
| #18 | .1695 | 4.31 | 51% |
| 11/64 | .1719 | 4.37 | 45% |
Neighboring sizes
Questions
What does #10-32 mean?
A #10 nominal diameter with 32 threads per inch. It’s the fine (UNF) thread for that size; the coarse version is #10-24.
Can I use a 4 mm drill instead of #21?
Usually. 4 mm is .1575″ against .1590″ for #21, 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.