UNFfine60° flankASME B1.1

1-1/4-12 UNF Thread Dimensions

1-1/4-12 UNF is a Unified National Fine thread. There are 12 threads per inch on a 1.25 in major diameter, giving a metric-equivalent pitch of 2.117 mm. The recommended tap drill is nominal diameter minus pitch.

Major Ø1.25 in

Threads per inch12

Pitch (metric)2.117 mm

Pitch Ø1.1961 in

Tap drill1.1667 in

Thread profile

millimetres unless stated

1-1/4-12 UNF — basic profile60° flank angle · Not to scale

Basic information

Designation: 1-1/4-12 UNF
Thread system: Unified National Fine
Series: fine
Standard: ASME B1.1
Basic profile: Unified basic profile
Flank angle: 60°

Dimensions

Major diameter: 1.25 in / 31.75 mm
Pitch (metric equivalent): 2.117 mm
Threads per inch: 12
Pitch diameter: 1.1961 in / 30.38 mm
Minor diameter (external): 1.1476 in / 29.15 mm
Minor diameter (internal): 1.1598 in / 29.46 mm
Thread depth: 0.0511 in / 1.298 mm
Recommended tap drill: Ø 1.1667 in / 29.633 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 1-1/4-12 UNF yet.

Neighbouring sizes in Unified National Fine.

3/4-16 UNF 7/8-14 UNF 1-12 UNF 1-1/8-12 UNF 1-1/2-12 UNF