Thread Pitch Reference
Thread Pitch & Size Reference Chart
Complete reference for Unified National (UNC/UNF) and Metric (ISO) thread specifications. Includes major diameter, threads per inch, tap drill sizes, and pitch dimensions.
Unified National Coarse (UNC) Thread
| Size | Major Dia (in) | TPI | Pitch (in) | Tap Drill | Clearance Drill |
|---|---|---|---|---|---|
| #2-56 | 0.086 | 56 | 0.0179 | #50 (0.070) | #42 (0.094) |
| #4-40 | 0.112 | 40 | 0.0250 | #43 (0.089) | #31 (0.120) |
| #6-32 | 0.138 | 32 | 0.0312 | #36 (0.107) | #27 (0.144) |
| #8-32 | 0.164 | 32 | 0.0312 | #29 (0.136) | #18 (0.170) |
| #10-24 | 0.190 | 24 | 0.0417 | #25 (0.150) | #9 (0.196) |
| #12-24 | 0.216 | 24 | 0.0417 | #16 (0.177) | #2 (0.221) |
| 1/4"-20 | 0.250 | 20 | 0.0500 | #7 (0.201) | 17/64 (0.266) |
| 5/16"-18 | 0.3125 | 18 | 0.0556 | F (0.257) | 21/64 (0.328) |
| 3/8"-16 | 0.375 | 16 | 0.0625 | 5/16 (0.3125) | 25/64 (0.391) |
| 7/16"-14 | 0.4375 | 14 | 0.0714 | U (0.368) | 29/64 (0.453) |
| 1/2"-13 | 0.500 | 13 | 0.0769 | 27/64 (0.422) | 17/32 (0.531) |
| 9/16"-12 | 0.5625 | 12 | 0.0833 | 31/64 (0.484) | 37/64 (0.578) |
| 5/8"-11 | 0.625 | 11 | 0.0909 | 17/32 (0.531) | 41/64 (0.641) |
| 3/4"-10 | 0.750 | 10 | 0.1000 | 21/32 (0.656) | 49/64 (0.766) |
| 7/8"-9 | 0.875 | 9 | 0.1111 | 49/64 (0.766) | 57/64 (0.891) |
| 1"-8 | 1.000 | 8 | 0.1250 | 7/8 (0.875) | 1-1/64 (1.016) |
Unified National Fine (UNF) Thread
| Size | Major Dia (in) | TPI | Pitch (in) | Tap Drill | Clearance Drill |
|---|---|---|---|---|---|
| #4-48 | 0.112 | 48 | 0.0208 | #42 (0.094) | #31 (0.120) |
| #6-40 | 0.138 | 40 | 0.0250 | #33 (0.113) | #27 (0.144) |
| #8-36 | 0.164 | 36 | 0.0278 | #29 (0.136) | #18 (0.170) |
| #10-32 | 0.190 | 32 | 0.0312 | #21 (0.159) | #9 (0.196) |
| 1/4"-28 | 0.250 | 28 | 0.0357 | #3 (0.213) | 17/64 (0.266) |
| 5/16"-24 | 0.3125 | 24 | 0.0417 | I (0.272) | 21/64 (0.328) |
| 3/8"-24 | 0.375 | 24 | 0.0417 | Q (0.332) | 25/64 (0.391) |
| 7/16"-20 | 0.4375 | 20 | 0.0500 | 25/64 (0.391) | 29/64 (0.453) |
| 1/2"-20 | 0.500 | 20 | 0.0500 | 29/64 (0.453) | 17/32 (0.531) |
| 9/16"-18 | 0.5625 | 18 | 0.0556 | 33/64 (0.516) | 37/64 (0.578) |
| 5/8"-18 | 0.625 | 18 | 0.0556 | 37/64 (0.578) | 41/64 (0.641) |
| 3/4"-16 | 0.750 | 16 | 0.0625 | 11/16 (0.688) | 49/64 (0.766) |
| 7/8"-14 | 0.875 | 14 | 0.0714 | 13/16 (0.812) | 57/64 (0.891) |
| 1"-14 | 1.000 | 14 | 0.0714 | 15/16 (0.938) | 1-1/64 (1.016) |
Metric Coarse Thread — ISO 261
| Size | Major Dia (mm) | Pitch (mm) | Tap Drill (mm) | US Equivalent |
|---|---|---|---|---|
| M3 × 0.5 | 3.00 | 0.50 | 2.50 | ~#4 |
| M4 × 0.7 | 4.00 | 0.70 | 3.30 | ~#8 |
| M5 × 0.8 | 5.00 | 0.80 | 4.20 | ~#10 |
| M6 × 1.0 | 6.00 | 1.00 | 5.00 | ~1/4" |
| M8 × 1.25 | 8.00 | 1.25 | 6.75 | ~5/16" |
| M10 × 1.5 | 10.00 | 1.50 | 8.50 | ~3/8" |
| M12 × 1.75 | 12.00 | 1.75 | 10.25 | ~1/2" |
| M14 × 2.0 | 14.00 | 2.00 | 12.00 | ~9/16" |
| M16 × 2.0 | 16.00 | 2.00 | 14.00 | ~5/8" |
| M20 × 2.5 | 20.00 | 2.50 | 17.50 | ~3/4" |
| M24 × 3.0 | 24.00 | 3.00 | 21.00 | ~1" |
| M30 × 3.5 | 30.00 | 3.50 | 26.50 | ~1-1/4" |
| M36 × 4.0 | 36.00 | 4.00 | 32.00 | ~1-1/2" |
Coarse Thread vs. Fine Thread
UNC / Coarse Thread
Deeper threads, wider spacing. More resistant to cross-threading and stripping. Better for softer materials (cast iron, aluminum). Easier assembly. Standard choice for most applications. Less affected by nicks and dings on threads.
UNF / Fine Thread
Shallower threads, closer spacing. Higher tensile strength (larger stress area). Better for precision adjustments and thin-wall applications. More susceptible to cross-threading. Requires more care during assembly. Used in automotive, aerospace, and vibration-sensitive applications.
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