1-3/8-6 UNC Thread Dimensions
1-3/8-6 UNC is a Unified National Coarse thread. There are 6 threads per inch on a 1.375 in major diameter, giving a metric-equivalent pitch of 4.233 mm. The recommended tap drill is nominal diameter minus pitch.
Thread profile
millimetres unless statedBasic information
- Designation
- 1-3/8-6 UNC
- Thread system
- Unified National Coarse
- Series
- coarse
- Standard
- ASME B1.1
- Basic profile
- Unified basic profile
- Flank angle
- 60°
Dimensions
- Major diameter
- 1.375 in / 34.925 mm
- Pitch (metric equivalent)
- 4.233 mm
- Threads per inch
- 6
- Pitch diameter
- 1.2669 in / 32.18 mm
- Minor diameter (external)
- 1.1705 in / 29.73 mm
- Minor diameter (internal)
- 1.1945 in / 30.34 mm
- Thread depth
- 0.1022 in / 2.597 mm
- Recommended tap drill
- Ø 1.2083 in / 30.692 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 1-3/8-6 UNC yet.
Related
Neighbouring sizes in Unified National Coarse.