#2-56 Tap Drill Size & Thread Specs
Everything for a #2-56 UNC thread on one page: tap drill (#50), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #2-56
#2-56 specs
SizePlate
#2-56 UNC · tap with
#50 drill
.0700″
1.78 mm · 69% thread
- Metric drill
- 1.8 mm · .0709
- Clearance
- #43 / #41
Thread
- Nominal size
- #2 · 2.18 mm
- Major diameter
- .0860″
- Threads per inch
- 56
- Pitch
- .0179″ · 0.454 mm
- Series
- UNC (coarse)
- UNF version
- #2-64
Drilling
- Tap drill (75%)
- #50 · .0700
- Metric substitute
- 1.8 mm · .0709
- Tap drill (≈50%)
- #49 · .0730
- Close fit
- #43 · .0890
- Free fit
- #41 · .0960
Nearest metric
- Thread
- M2 × 0.4
- Major diameter
- 2 mm
- Pitch
- 0.4 mm
- Tap drill
- 1.6 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 |
|---|---|---|---|
| 1.7 mm | .0669 | 1.7 | 82% |
| #51 | .0670 | 1.7 | 82% |
| #50 | .0700 | 1.78 | 69% |
| 1.8 mm | .0709 | 1.8 | 65% |
| #49 | .0730 | 1.85 | 56% |
| 1.9 mm | .0748 | 1.9 | 48% |
Neighboring sizes
Questions
What does #2-56 mean?
A #2 nominal diameter with 56 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is #2-64.
Can I use a 1.8 mm drill instead of #50?
Usually. 1.8 mm is .0709″ against .0700″ for #50, 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.