#10-32 UNF Thread
Recommended tap drill #21
Tap drill Ø 0.1590″ / 4.039 mm
Major Ø 0.1900″ / 4.826 mm
Threads per inch 32
The chart recommendation gives approximately 76.4% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #10-32 UNF |
|---|---|
| Thread family | Unified National Fine (UNF) |
| Nominal size | #10 |
| Basic major diameter | 0.1900″ / 4.826 mm |
| Threads per inch / pitch | 32 TPI (0.794 mm pitch) |
| Recommended tap drill | #21 (0.1590″ / 4.039 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #10-32 UNF; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 5/32″ | 0.1563 | 3.969 | 83.1% |
| #22 | 0.1570 | 3.988 | 81.3% |
| 4 mm | 0.1575 | 4 | 80.1% |
| #21 — chart recommendation | 0.1590 | 4.039 | 76.4% |
| #20 | 0.1610 | 4.089 | 71.4% |
| 4.1 mm | 0.1614 | 4.1 | 70.4% |
| 4.2 mm | 0.1654 | 4.2 | 60.7% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #21 | Resulting engagement |
|---|---|---|---|
| 4 mm | 0.1575″ / 4 mm | −0.039 mm | 80.1% |
| 5/32″ | 0.1563″ / 3.969 mm | −0.07 mm | 83.1% |
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
- #10-24 UNC — same nominal size, 24 TPI (Unified National Coarse (UNC)) · compare
- #8-36 UNF — next size down in UNF
- #12-28 UNF — next size up in UNF