UNC Unified Coarse Thread · ANSI/ASME B1.1
3 1/2" - 4 UNC Thread: Pitch, Tap Drill & Dimensions
3 1/2" - 4 UNC is a UNC Unified Coarse Thread (ANSI/ASME B1.1) size, with a major diameter of 88.900 mm, 4 threads per inch (6.350 mm pitch). The tap drill is 82.41 mm.
| Major Diameter (inch) | 3.500 |
|---|---|
| Major Diameter (mm) | 88.900 |
| Tapping Drill Size (mm) | 82.41 |
| TPI | 4 |
| Pitch (mm) | 6.350 |
| Flank angle | 60° |
Common questions
What size drill do I use to tap 3 1/2" - 4 UNC?
Use a 82.41 drill. This is the standard tap drill for 3 1/2" - 4 UNC; for hard materials or deep threads a slightly larger drill reduces tapping torque.
What is the pitch of 3 1/2" - 4 UNC?
The pitch of 3 1/2" - 4 UNC is 6.350, meaning the thread advances that distance in one full turn.
Where can I find other UNC Unified Coarse Thread sizes?
The full UNC Unified Coarse Thread table, with every size and a live filter, is on its standard page, and the Thread Finder searches all 73 standards at once.
Reference values; computed values use the ISO basic profile. Verify against the current standard before production use.