5/8-18 UNF Thread Dimensions
5/8-18 UNF is a Unified National Fine thread. There are 18 threads per inch on a 0.625 in major diameter, giving a metric-equivalent pitch of 1.411 mm. The recommended tap drill is nominal diameter minus pitch.
Thread profile
millimetres unless statedBasic information
- Designation
- 5/8-18 UNF
- Thread system
- Unified National Fine
- Series
- fine
- Standard
- ASME B1.1
- Basic profile
- Unified basic profile
- Flank angle
- 60°
Dimensions
- Major diameter
- 0.625 in / 15.875 mm
- Pitch (metric equivalent)
- 1.411 mm
- Threads per inch
- 18
- Pitch diameter
- 0.589 in / 14.96 mm
- Minor diameter (external)
- 0.5567 in / 14.14 mm
- Minor diameter (internal)
- 0.565 in / 14.35 mm
- Thread depth
- 0.0341 in / 0.866 mm
- Recommended tap drill
- Ø 0.5694 in / 14.464 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 5/8-18 UNF yet.
Related
Neighbouring sizes in Unified National Fine.