#10-24 Tap Drill Size & Thread Specs
Everything for a #10-24 UNC thread on one page: tap drill (#25), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #10-24
#10-24 specs
SizePlate
#10-24 UNC · tap with
#25 drill
.1495″
3.8 mm · 75% thread
- Metric drill
- 3.8 mm · .1496
- Clearance
- #9 / #7
- Wrench
- 3/8″
- Cap screw key
- 5/32″
Thread
- Nominal size
- #10 · 4.83 mm
- Major diameter
- .1900″
- Threads per inch
- 24
- Pitch
- .0417″ · 1.058 mm
- Series
- UNC (coarse)
- UNF version
- #10-32
Drilling
- Tap drill (75%)
- #25 · .1495
- Metric substitute
- 3.8 mm · .1496
- Tap drill (≈50%)
- #20 · .1610
- 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 |
|---|---|---|---|
| #27 | .1440 | 3.66 | 85% |
| 3.7 mm | .1457 | 3.7 | 82% |
| #26 | .1470 | 3.73 | 79% |
| #25 | .1495 | 3.8 | 75% |
| 3.8 mm | .1496 | 3.8 | 75% |
| #24 | .1520 | 3.86 | 70% |
| 3.9 mm | .1535 | 3.9 | 67% |
| #23 | .1540 | 3.91 | 67% |
| 5/32 | .1563 | 3.97 | 62% |
| #22 | .1570 | 3.99 | 61% |
| 4 mm | .1575 | 4 | 60% |
| #21 | .1590 | 4.04 | 57% |
| #20 | .1610 | 4.09 | 54% |
| 4.1 mm | .1614 | 4.1 | 53% |
| 4.2 mm | .1654 | 4.2 | 46% |
Neighboring sizes
Questions
What does #10-24 mean?
A #10 nominal diameter with 24 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is #10-32.
Can I use a 3.8 mm drill instead of #25?
Usually. 3.8 mm is .1496″ against .1495″ for #25, 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.