UNCcoarse60° flankASME B1.1

#2-56 UNC Thread Dimensions

#2-56 UNC is a coarse Unified National Coarse thread. There are 56 threads per inch on a 0.0858 in major diameter, giving a metric-equivalent pitch of 0.454 mm. The recommended tap drill leaves roughly 75% thread engagement.

Major Ø0.0858 in
Threads per inch56
Pitch (metric)0.454 mm
Pitch Ø0.0744 in
Tap drill0.0681 in

Thread profile

millimetres unless stated
Thread profile — #2-56 UNCd 2.18d2 1.89d3 1.63mm60°P 0.454h3 0.278tap ⌀1.73
#2-56 UNC — basic profile60° flank angle · Not to scale

Basic information

Designation
#2-56 UNC
Thread system
Unified National Coarse
Series
coarse
Standard
ASME B1.1
Basic profile
Unified basic profile
Flank angle
60°

Dimensions

Major diameter
0.0858 in / 2.18 mm
Pitch (metric equivalent)
0.454 mm
Threads per inch
56
Pitch diameter
0.0744 in / 1.89 mm
Minor diameter (external)
0.0642 in / 1.63 mm
Minor diameter (internal)
0.0665 in / 1.69 mm
Thread depth
0.0109 in / 0.278 mm
Recommended tap drill
Ø 0.0681 in / 1.73 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 #2-56 UNC yet.

Related

Neighbouring sizes in Unified National Coarse.

#1-64 UNC#3-48 UNC#4-40 UNC#5-40 UNC#6-32 UNC