#10-24 UNC Thread
Recommended tap drill #25
Tap drill Ø 0.1495″ / 3.797 mm
Major Ø 0.1900″ / 4.826 mm
Threads per inch 24
The chart recommendation gives approximately 74.8% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #10-24 UNC |
|---|---|
| Thread family | Unified National Coarse (UNC) |
| Nominal size | #10 |
| Basic major diameter | 0.1900″ / 4.826 mm |
| Threads per inch / pitch | 24 TPI (1.058 mm pitch) |
| Recommended tap drill | #25 (0.1495″ / 3.797 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #10-24 UNC; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| #27 | 0.1440 | 3.658 | 85% |
| 3.7 mm | 0.1457 | 3.7 | 81.9% |
| #26 | 0.1470 | 3.734 | 79.4% |
| #25 — chart recommendation | 0.1495 | 3.797 | 74.8% |
| 3.8 mm | 0.1496 | 3.8 | 74.6% |
| #24 | 0.1520 | 3.861 | 70.2% |
| 3.9 mm | 0.1535 | 3.9 | 67.4% |
| #23 | 0.1540 | 3.912 | 66.5% |
| 5/32″ | 0.1563 | 3.969 | 62.4% |
| #22 | 0.1570 | 3.988 | 61% |
| 4 mm | 0.1575 | 4 | 60.1% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #25 | Resulting engagement |
|---|---|---|---|
| 3.8 mm | 0.1496″ / 3.8 mm | +0.003 mm | 74.6% |
| 5/32″ | 0.1563″ / 3.969 mm | +0.171 mm | 62.4% |
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
- #10-32 UNF — same nominal size, 32 TPI (Unified National Fine (UNF)) · compare
- #8-32 UNC — next size down in UNC
- #12-24 UNC — next size up in UNC