#12-28 Tap Drill Size & Thread Specs
Everything for a #12-28 UNF thread on one page: tap drill (#14), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #12-28
#12-28 specs
SizePlate
#12-28 UNF · tap with
#14 drill
.1820″
4.62 mm · 73% thread
- Metric drill
- 4.6 mm · .1811
- Clearance
- #2 / #1
Thread
- Nominal size
- #12 · 5.49 mm
- Major diameter
- .2160″
- Threads per inch
- 28
- Pitch
- .0357″ · 0.907 mm
- Series
- UNF (fine)
- UNC version
- #12-24
Drilling
- Tap drill (75%)
- #14 · .1820
- Metric substitute
- 4.6 mm · .1811
- Tap drill (≈50%)
- #10 · .1935
- 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 |
|---|---|---|---|
| #16 | .1770 | 4.5 | 84% |
| 4.5 mm | .1772 | 4.5 | 84% |
| #15 | .1800 | 4.57 | 78% |
| 4.6 mm | .1811 | 4.6 | 75% |
| #14 | .1820 | 4.62 | 73% |
| #13 | .1850 | 4.7 | 67% |
| 4.7 mm | .1850 | 4.7 | 67% |
| 3/16 | .1875 | 4.76 | 61% |
| 4.8 mm | .1890 | 4.8 | 58% |
| #12 | .1890 | 4.8 | 58% |
| #11 | .1910 | 4.85 | 54% |
| 4.9 mm | .1929 | 4.9 | 50% |
| #10 | .1935 | 4.91 | 48% |
Neighboring sizes
Questions
What does #12-28 mean?
A #12 nominal diameter with 28 threads per inch. It’s the fine (UNF) thread for that size; the coarse version is #12-24.
Can I use a 4.6 mm drill instead of #14?
Usually. 4.6 mm is .1811″ against .1820″ for #14, 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.