#2-56 UNC Thread
Recommended tap drill #50
Tap drill Ø 0.0700″ / 1.778 mm
Major Ø 0.0860″ / 2.184 mm
Threads per inch 56
The chart recommendation gives approximately 69% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #2-56 UNC |
|---|---|
| Thread family | Unified National Coarse (UNC) |
| Nominal size | #2 |
| Basic major diameter | 0.0860″ / 2.184 mm |
| Threads per inch / pitch | 56 TPI (0.454 mm pitch) |
| Recommended tap drill | #50 (0.0700″ / 1.778 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #2-56 UNC; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 1.7 mm | 0.0669 | 1.7 | 82.2% |
| #51 | 0.0670 | 1.702 | 81.9% |
| #50 — chart recommendation | 0.0700 | 1.778 | 69% |
| 1.8 mm | 0.0709 | 1.8 | 65.2% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #50 | Resulting engagement |
|---|---|---|---|
| 1.8 mm | 0.0709″ / 1.8 mm | +0.022 mm | 65.2% |
Clearance holes
For a bolt or screw of this size to pass through freely. Recommended drills per ASME B18.2.8: close, normal, and loose fits.
Related threads
- #2-64 UNF — same nominal size, 64 TPI (Unified National Fine (UNF)) · compare
- #1-64 UNC — next size down in UNC
- #3-48 UNC — next size up in UNC