7/8-20 UNEF Thread Dimensions
7/8-20 UNEF is a Unified National Extra Fine thread. There are 20 threads per inch on a 0.875 in major diameter, giving a metric-equivalent pitch of 1.27 mm. The recommended tap drill is nominal diameter minus pitch.
Thread profile
millimetres unless statedBasic information
- Designation
- 7/8-20 UNEF
- Thread system
- Unified National Extra Fine
- Series
- extra fine
- Standard
- ASME B1.1
- Basic profile
- Unified basic profile
- Flank angle
- 60°
Dimensions
- Major diameter
- 0.875 in / 22.225 mm
- Pitch (metric equivalent)
- 1.27 mm
- Threads per inch
- 20
- Pitch diameter
- 0.8425 in / 21.4 mm
- Minor diameter (external)
- 0.8138 in / 20.67 mm
- Minor diameter (internal)
- 0.8209 in / 20.85 mm
- Thread depth
- 0.0307 in / 0.779 mm
- Recommended tap drill
- Ø 0.825 in / 20.955 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 parts0 specification pages
No specification in this database uses 7/8-20 UNEF yet.
Related
Neighbouring sizes in Unified National Extra Fine.