UNCcoarse60° flank

#2-56 UNC Thread Dimensions

#2-56 UNC is a coarse pitch UNC thread. There are 56 threads per inch, giving a pitch of 0.45 mm. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø2.18 mm
Pitch0.45 mm
Threads per inch56
Pitch Ø-5.3 mm
Tap drill-9.34 mm

Thread profile

millimetres unless stated
Thread profile — #2-56 UNCd 2.18d2 -5.3d3 -11.95mm60°P 0.45h3 7.07tap ⌀-9.34
#2-56 UNC — basic profile60° flank angle · Not to scale
Designation
#2-56 UNC
Thread system
UNC
Series
coarse
Flank angle
60°
Major diameter
2.18 mm / 0.09"
Pitch
0.45 mm
Threads per inch
56
Pitch diameter
-5.3 mm
Minor diameter (external)
-11.95 mm
Minor diameter (internal)
-10.29 mm
Thread depth
7.07 mm
Recommended tap drill
Ø -9.34 mm / -0.3676"

How these values are derived

Basic ISO thread geometry uses the fundamental triangle height H = 0.866025 × P. External minor diameter d₃ = d − 1.226869 × P, internal minor diameter D₁ = d − 1.082532 × P. Tap drill is given as nominal diameter minus pitch, which approximates a 75% thread engagement — adjust for tough materials or deep holes.