UNFfine60° flankASME B1.1

#3-56 UNF Thread Dimensions

#3-56 UNF is a fine Unified National Fine thread. There are 56 threads per inch on a 0.0988 in major diameter, giving a metric-equivalent pitch of 0.454 mm. The recommended tap drill leaves roughly 75% thread engagement.

Major Ø0.0988 in
Threads per inch56
Pitch (metric)0.454 mm
Pitch Ø0.0874 in
Tap drill0.0811 in

Thread profile

millimetres unless stated
Thread profile — #3-56 UNFd 2.51d2 2.22d3 1.96mm60°P 0.454h3 0.278tap ⌀2.06
#3-56 UNF — basic profile60° flank angle · Not to scale

Basic information

Designation
#3-56 UNF
Thread system
Unified National Fine
Series
fine
Standard
ASME B1.1
Basic profile
Unified basic profile
Flank angle
60°

Dimensions

Major diameter
0.0988 in / 2.51 mm
Pitch (metric equivalent)
0.454 mm
Threads per inch
56
Pitch diameter
0.0874 in / 2.22 mm
Minor diameter (external)
0.0772 in / 1.96 mm
Minor diameter (internal)
0.0795 in / 2.02 mm
Thread depth
0.0109 in / 0.278 mm
Recommended tap drill
Ø 0.0811 in / 2.06 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 #3-56 UNF yet.

Related

Neighbouring sizes in Unified National Fine.

#0-80 UNF#1-72 UNF#2-64 UNF#4-48 UNF#5-44 UNF#6-40 UNF#8-36 UNF