#4-40 UNC Thread Dimensions
#4-40 UNC is a Unified National Coarse thread. There are 40 threads per inch on a 0.112 in major diameter, giving a metric-equivalent pitch of 0.635 mm. The recommended tap drill is nominal diameter minus pitch.
Thread profile
millimetres unless statedBasic information
- Designation
- #4-40 UNC
- Thread system
- Unified National Coarse
- Series
- coarse
- Standard
- ASME B1.1
- Basic profile
- Unified basic profile
- Flank angle
- 60°
Dimensions
- Major diameter
- 0.112 in / 2.845 mm
- Pitch (metric equivalent)
- 0.635 mm
- Threads per inch
- 40
- Pitch diameter
- 0.0957 in / 2.43 mm
- Minor diameter (external)
- 0.0815 in / 2.07 mm
- Minor diameter (internal)
- 0.085 in / 2.16 mm
- Thread depth
- 0.0154 in / 0.39 mm
- Recommended tap drill
- Ø 0.087 in / 2.21 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 parts6 specification pages
All 4-40 fastenersEvery fastener below is threaded #4-40 UNC, so a nut, bolt or washer picked from this list will mate with it.
Related
Neighbouring sizes in Unified National Coarse.