Home › Tap drill chart › #2-56
#2-56 tap drill size
Use a #50 drill (.0700 in / 1.78 mm) to tap #2-56 UNC. That gives about 69% thread engagement. Closest metric drill: 1.8 mm.
#2-56 thread specifications
| Thread | #2-56 UNC (coarse) |
|---|---|
| Major (nominal) diameter | .0860 in / 2.18 mm |
| Threads per inch | 56 (pitch 0.454 mm) |
| Theoretical drill for 75% thread | .0686 in (1.74 mm) |
| Recommended tap drill | #50 = .0700 in |
Alternative drills and % of thread
Any of these drills will tap #2-56. Smaller drills give more thread but make tapping harder and raise the risk of breaking the tap, especially in stainless steel and in small sizes. 60–65% thread is common in tough materials. 75% is the general-purpose standard.
Tips for tapping #2-56
- Use cutting fluid, and with a hand tap back off about half a turn every turn or two to break the chip. Aluminium and soft materials are the exception: they tap cleanly with spiral-point taps.
- For blind holes, drill deeper than the thread you need. Allow at least 3–4 pitches beyond the last full thread for a plug tap (0.071" for 56 TPI).
- Thread engagement of 1–1.5 × the diameter (2.2–3.3 mm) is enough for most steel parts. Softer materials need more.