UNF Tap Drill Sizes
UNF (Unified National Fine) threads have more threads per inch than UNC for the same diameter. They’re stronger in thin-walled parts, provide finer adjustment, and resist vibration loosening better — but they’re less forgiving and easier to cross-thread.
| Thread Size | TPI | Tap Drill | Decimal (in) | 75% Thread | Clearance Drill |
|---|---|---|---|---|---|
| #0-80 | 80 | 3/64 | 0.0469 | 0.0469 | #51 (0.067) |
| #1-72 | 72 | #53 | 0.0595 | 0.0595 | #46 (0.081) |
| #2-64 | 64 | #50 | 0.0700 | 0.0700 | #43 (0.089) |
| #3-56 | 56 | #45 | 0.0820 | 0.0820 | #37 (0.104) |
| #4-48 | 48 | #42 | 0.0935 | 0.0935 | #32 (0.116) |
| #6-40 | 40 | #33 | 0.1130 | 0.1130 | #27 (0.144) |
| #8-36 | 36 | #29 | 0.1360 | 0.1360 | #18 (0.170) |
| #10-32 | 32 | #21 | 0.1590 | 0.1590 | #9 (0.196) |
| #12-28 | 28 | #14 | 0.1820 | 0.1820 | #2 (0.221) |
| 1/4-28 | 28 | #3 | 0.2130 | 0.2130 | 17/64 (0.266) |
| 5/16-24 | 24 | I | 0.2720 | 0.2720 | 21/64 (0.328) |
| 3/8-24 | 24 | Q | 0.3320 | 0.3320 | 25/64 (0.391) |
| 7/16-20 | 20 | 25/64 | 0.3906 | 0.3906 | 29/64 (0.453) |
| 1/2-20 | 20 | 29/64 | 0.4531 | 0.4531 | 17/32 (0.531) |
| 9/16-18 | 18 | 33/64 | 0.5156 | 0.5156 | 19/32 (0.594) |
| 5/8-18 | 18 | 37/64 | 0.5781 | 0.5781 | 21/32 (0.656) |
| 3/4-16 | 16 | 11/16 | 0.6875 | 0.6875 | 25/32 (0.781) |
| 7/8-14 | 14 | 13/16 | 0.8125 | 0.8125 | 29/32 (0.906) |
| 1-12 | 12 | 15/16 | 0.9375 | 0.9375 | 1-1/16 (1.063) |
| 1-1/4-12 | 12 | 1-11/64 | 1.1719 | 1.1719 | 1-5/16 (1.313) |
| 1-1/2-12 | 12 | 1-27/64 | 1.4219 | 1.4219 | 1-9/16 (1.563) |
UNF vs. UNC — When to Choose Fine
- Thin-walled parts: More threads in less length = more engagement before you punch through
- Vibration resistance: Fine threads have a smaller helix angle, so they resist loosening better
- Adjustment screws: Finer pitch = more precise positioning per turn
- Higher tensile strength: Larger minor diameter for the same nominal size
Related: UNC Tap Drill Sizes | UNF Thread Dimensions | Metric Tap Drill Chart