5/8-18 UNF Thread Dimensions
5/8-18 UNF is a fine Unified National Fine thread. There are 18 threads per inch on a 0.6252 in major diameter, giving a metric-equivalent pitch of 1.411 mm. The recommended tap drill leaves roughly 75% thread engagement.
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
- 0.6252 in / 15.88 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 0.5693 in / 14.46 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 uses a fundamental triangle height H = 0.866025 × P, with external minor diameter d₃ = d − 1.226869 × P and internal minor diameter D₁ = d − 1.082532 × P; the two differ because the external root is rounded while the internal crest is truncated. A 55° Whitworth profile uses H = 0.960491 × P and a thread height of 0.640327 × P. 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.