UNFfine60° flankASME B1.1

#6-40 UNF Thread Dimensions

#6-40 UNF is a fine Unified National Fine thread. There are 40 threads per inch on a 0.1382 in major diameter, giving a metric-equivalent pitch of 0.635 mm. The recommended tap drill leaves roughly 75% thread engagement.

Major Ø0.1382 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: 0.1382 in / 3.51 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 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 #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