#12-24 UNC Thread
Recommended tap drill #16
Tap drill Ø 0.1770″ / 4.496 mm
Major Ø 0.2160″ / 5.486 mm
Threads per inch 24
The chart recommendation gives approximately 72.1% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #12-24 UNC |
|---|---|
| Thread family | Unified National Coarse (UNC) |
| Nominal size | #12 |
| Basic major diameter | 0.2160″ / 5.486 mm |
| Threads per inch / pitch | 24 TPI (1.058 mm pitch) |
| Recommended tap drill | #16 (0.1770″ / 4.496 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #12-24 UNC; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 11/64″ | 0.1719 | 4.366 | 81.5% |
| #17 | 0.1730 | 4.394 | 79.4% |
| 4.4 mm | 0.1732 | 4.4 | 79% |
| #16 — chart recommendation | 0.1770 | 4.496 | 72.1% |
| 4.5 mm | 0.1772 | 4.5 | 71.7% |
| #15 | 0.1800 | 4.572 | 66.5% |
| 4.6 mm | 0.1811 | 4.6 | 64.5% |
| #14 | 0.1820 | 4.623 | 62.8% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #16 | Resulting engagement |
|---|---|---|---|
| 4.5 mm | 0.1772″ / 4.5 mm | +0.004 mm | 71.7% |
| 11/64″ | 0.1719″ / 4.366 mm | −0.13 mm | 81.5% |
Related threads
- #12-28 UNF — same nominal size, 28 TPI (Unified National Fine (UNF)) · compare
- #10-24 UNC — next size down in UNC
- 1/4″-20 UNC — next size up in UNC