#3-56 UNF Thread
Recommended tap drill #45
Tap drill Ø 0.0820″ / 2.083 mm
Major Ø 0.0990″ / 2.515 mm
Threads per inch 56
The chart recommendation gives approximately 73.3% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #3-56 UNF |
|---|---|
| Thread family | Unified National Fine (UNF) |
| Nominal size | #3 |
| Basic major diameter | 0.0990″ / 2.515 mm |
| Threads per inch / pitch | 56 TPI (0.454 mm pitch) |
| Recommended tap drill | #45 (0.0820″ / 2.083 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #3-56 UNF; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 2.05 mm | 0.0807 | 2.05 | 78.9% |
| #46 | 0.0810 | 2.057 | 77.6% |
| #45 — chart recommendation | 0.0820 | 2.083 | 73.3% |
| 2.1 mm | 0.0827 | 2.1 | 70.4% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #45 | Resulting engagement |
|---|---|---|---|
| 2.1 mm | 0.0827″ / 2.1 mm | +0.017 mm | 70.4% |
| 5/64″ | 0.0781″ / 1.984 mm | −0.098 mm | 90% |
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
- #3-48 UNC — same nominal size, 48 TPI (Unified National Coarse (UNC)) · compare
- #2-64 UNF — next size down in UNF
- #4-48 UNF — next size up in UNF