Thread Pitch Reference Chart
Standard UNC and UNF threads per inch, and ISO metric coarse pitch, for the sizes that come up most often on the floor.
Imperial: UNC & UNF
| Size | UNC (coarse) | UNF (fine) |
|---|---|---|
| #4 | 40 TPI | 48 TPI |
| #6 | 32 TPI | 40 TPI |
| #8 | 32 TPI | 36 TPI |
| #10 | 24 TPI | 32 TPI |
| 1/4" | 20 TPI | 28 TPI |
| 5/16" | 18 TPI | 24 TPI |
| 3/8" | 16 TPI | 24 TPI |
| 7/16" | 14 TPI | 20 TPI |
| 1/2" | 13 TPI | 20 TPI |
| 9/16" | 12 TPI | 18 TPI |
| 5/8" | 11 TPI | 18 TPI |
| 3/4" | 10 TPI | 16 TPI |
| 7/8" | 9 TPI | 14 TPI |
| 1" | 8 TPI | 12 TPI |
Metric: ISO Coarse
| Size | Pitch (mm) |
|---|---|
| M3 | 0.50 |
| M4 | 0.70 |
| M5 | 0.80 |
| M6 | 1.00 |
| M8 | 1.25 |
| M10 | 1.50 |
| M12 | 1.75 |
| M14 | 2.00 |
| M16 | 2.00 |
| M20 | 2.50 |
| M24 | 3.00 |
Fine-pitch metric threads exist for most of these sizes too (e.g. M10×1.25); this chart lists the coarse (default) pitch used unless a print specifies fine.
Coarse vs. fine, and when to reach for which
Coarse threads (UNC, ISO coarse) are the default choice for most general work — they're faster to run, more tolerant of dirt and minor thread damage, and less prone to cross-threading or galling in softer materials. Fine threads (UNF) give a larger minor diameter for the same major diameter, which means more thread shear area and a stronger fastener in thin-walled or hardened parts, at the cost of being slower to run and less forgiving of damaged threads or contamination.
Feeding this into other calculators
The TPI or pitch values here are exactly what the Tap Drill Size Calculator and Thread Depth Calculator need as inputs — look up the thread here first if you don't already have it memorized, then carry the number straight into either of those tools.