7/8-9 UNC Thread Dimensions
7/8-9 UNC is a Unified National Coarse thread. There are 9 threads per inch on a 0.875 in major diameter, giving a metric-equivalent pitch of 2.822 mm. The recommended tap drill is nominal diameter minus pitch.
Thread profile
millimetres unless statedBasic information
- Designation
- 7/8-9 UNC
- Thread system
- Unified National Coarse
- Series
- coarse
- Standard
- ASME B1.1
- Basic profile
- Unified basic profile
- Flank angle
- 60°
Dimensions
- Major diameter
- 0.875 in / 22.225 mm
- Pitch (metric equivalent)
- 2.822 mm
- Threads per inch
- 9
- Pitch diameter
- 0.8028 in / 20.39 mm
- Minor diameter (external)
- 0.7386 in / 18.76 mm
- Minor diameter (internal)
- 0.7547 in / 19.17 mm
- Thread depth
- 0.0681 in / 1.731 mm
- Recommended tap drill
- Ø 0.7639 in / 19.403 mm
How these values are derived
computed from the basic profileThese figures follow the Unified basic profile of ASME B1.1. A 60° basic profile has a fundamental triangle height H = 0.866025 × P, with pitch diameter d₂ = d − 0.649519 × P, external minor diameter d₃ = d − 1.226869 × P and internal minor diameter D₁ = d − 1.082532 × P; the two minor diameters differ because the external root is rounded while the internal crest is truncated. The recommended tap drill is given as nominal diameter minus pitch, which approximates 75% thread engagement — adjust it for tough materials or deep holes.
Compatible parts7 specification pages
All 7/8-9 fastenersEvery fastener below is threaded 7/8-9 UNC, so a nut, bolt or washer picked from this list will mate with it.
The dash in the Length column marks a nut or a washer: those parts have no length to quote, so the dash means not applicable rather than missing data.
Related
Neighbouring sizes in Unified National Coarse.