UNFfine60° flankASME B1.1

#6-40 UNF Thread Dimensions

#6-40 UNF is a Unified National Fine thread. There are 40 threads per inch on a 0.138 in major diameter, giving a metric-equivalent pitch of 0.635 mm. The recommended tap drill is nominal diameter minus pitch.

Major Ø0.138 in

Threads per inch40

Pitch (metric)0.635 mm

Pitch Ø0.1217 in

Tap drill0.113 in

Thread profile

millimetres unless stated

#6-40 UNF — basic profile60° flank angle · Not to scale

Basic information

Designation: #6-40 UNF
Thread system: Unified National Fine
Series: fine
Standard: ASME B1.1
Basic profile: Unified basic profile
Flank angle: 60°

Dimensions

Major diameter: 0.138 in / 3.505 mm
Pitch (metric equivalent): 0.635 mm
Threads per inch: 40
Pitch diameter: 0.1217 in / 3.09 mm
Minor diameter (external): 0.1075 in / 2.73 mm
Minor diameter (internal): 0.111 in / 2.82 mm
Thread depth: 0.0154 in / 0.39 mm
Recommended tap drill: Ø 0.113 in / 2.87 mm

How these values are derived

computed from the basic profile

These 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 #6-40 UNF yet.

Neighbouring sizes in Unified National Fine.

#2-64 UNF #3-56 UNF #4-48 UNF #5-44 UNF #8-36 UNF #10-32 UNF #12-28 UNF 1/4-28 UNF