#4-40 UNC Thread
Recommended tap drill #43
Tap drill Ø 0.0890″ / 2.261 mm
Major Ø 0.1120″ / 2.845 mm
Threads per inch 40
The chart recommendation gives approximately 70.8% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #4-40 UNC |
|---|---|
| Thread family | Unified National Coarse (UNC) |
| Nominal size | #4 |
| Basic major diameter | 0.1120″ / 2.845 mm |
| Threads per inch / pitch | 40 TPI (0.635 mm pitch) |
| Recommended tap drill | #43 (0.0890″ / 2.261 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #4-40 UNC; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| #44 | 0.0860 | 2.184 | 80.1% |
| 2.2 mm | 0.0866 | 2.2 | 78.2% |
| #43 — chart recommendation | 0.0890 | 2.261 | 70.8% |
| 2.3 mm | 0.0906 | 2.3 | 66% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #43 | Resulting engagement |
|---|---|---|---|
| 2.3 mm | 0.0906″ / 2.3 mm | +0.039 mm | 66% |
| 3/32″ | 0.0938″ / 2.381 mm | +0.121 mm | 56.2% |
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
- #4-48 UNF — same nominal size, 48 TPI (Unified National Fine (UNF)) · compare
- #3-48 UNC — next size down in UNC
- #5-40 UNC — next size up in UNC