UNCcoarse60° flank

1-1/2-6 UNC Thread Dimensions

1-1/2-6 UNC is a coarse pitch UNC thread. There are 6 threads per inch, giving a pitch of 4.23 mm. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø38.1 mm
Pitch4.23 mm
Threads per inch6
Pitch Ø-31.74 mm
Tap drill-69.43 mm

Thread profile

millimetres unless stated
Thread profile — 1-1/2-6 UNCd 38.1d2 -31.74d3 -93.82mm60°P 4.23h3 65.96tap ⌀-69.43
1-1/2-6 UNC — basic profile60° flank angle · Not to scale
Designation
1-1/2-6 UNC
Thread system
UNC
Series
coarse
Flank angle
60°
Major diameter
38.1 mm / 1.5"
Pitch
4.23 mm
Threads per inch
6
Pitch diameter
-31.74 mm
Minor diameter (external)
-93.82 mm
Minor diameter (internal)
-78.3 mm
Thread depth
65.96 mm
Recommended tap drill
Ø -69.43 mm / -2.7333"

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.