#12-24 Tap Drill Size & Thread Specs
Everything for a #12-24 UNC thread on one page: tap drill (#16), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #12-24
#12-24 specs
SizePlate
#12-24 UNC · tap with
#16 drill
.1770″
4.5 mm · 72% thread
- Metric drill
- 4.5 mm · .1772
- Clearance
- #2 / #1
Thread
- Nominal size
- #12 · 5.49 mm
- Major diameter
- .2160″
- Threads per inch
- 24
- Pitch
- .0417″ · 1.058 mm
- Series
- UNC (coarse)
- UNF version
- #12-28
Drilling
- Tap drill (75%)
- #16 · .1770
- Metric substitute
- 4.5 mm · .1772
- Tap drill (≈50%)
- #12 · .1890
- Close fit
- #2 · .2210
- Free fit
- #1 · .2280
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 |
|---|---|---|---|
| 11/64 | .1719 | 4.37 | 81% |
| #17 | .1730 | 4.39 | 79% |
| 4.4 mm | .1732 | 4.4 | 79% |
| #16 | .1770 | 4.5 | 72% |
| 4.5 mm | .1772 | 4.5 | 72% |
| #15 | .1800 | 4.57 | 67% |
| 4.6 mm | .1811 | 4.6 | 64% |
| #14 | .1820 | 4.62 | 63% |
| #13 | .1850 | 4.7 | 57% |
| 4.7 mm | .1850 | 4.7 | 57% |
| 3/16 | .1875 | 4.76 | 53% |
| 4.8 mm | .1890 | 4.8 | 50% |
| #12 | .1890 | 4.8 | 50% |
| #11 | .1910 | 4.85 | 46% |
Neighboring sizes
Questions
What does #12-24 mean?
A #12 nominal diameter with 24 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is #12-28.
Can I use a 4.5 mm drill instead of #16?
Usually. 4.5 mm is .1772″ against .1770″ for #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.