#8-36 UNF Thread
Recommended tap drill #29
Tap drill Ø 0.1360″ / 3.454 mm
Major Ø 0.1640″ / 4.166 mm
Threads per inch 36
The chart recommendation gives approximately 77.6% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | #8-36 UNF |
|---|---|
| Thread family | Unified National Fine (UNF) |
| Nominal size | #8 |
| Basic major diameter | 0.1640″ / 4.166 mm |
| Threads per inch / pitch | 36 TPI (0.706 mm pitch) |
| Recommended tap drill | #29 (0.1360″ / 3.454 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for #8-36 UNF; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 3.4 mm | 0.1339 | 3.4 | 83.5% |
| #29 — chart recommendation | 0.1360 | 3.454 | 77.6% |
| 3.5 mm | 0.1378 | 3.5 | 72.6% |
| #28 | 0.1405 | 3.569 | 65.1% |
| 9/64″ | 0.1406 | 3.572 | 64.8% |
| 3.6 mm | 0.1417 | 3.6 | 61.7% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs #29 | Resulting engagement |
|---|---|---|---|
| 3.5 mm | 0.1378″ / 3.5 mm | +0.046 mm | 72.6% |
| 9/64″ | 0.1406″ / 3.572 mm | +0.117 mm | 64.8% |
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
- #8-32 UNC — same nominal size, 32 TPI (Unified National Coarse (UNC)) · compare
- #6-40 UNF — next size down in UNF
- #10-32 UNF — next size up in UNF