UNCcoarse60° flank

#1-64 UNC Thread Dimensions

#1-64 UNC is a coarse pitch UNC thread. There are 64 threads per inch, giving a pitch of 0.4 mm. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø1.85 mm
Pitch0.4 mm
Threads per inch64
Pitch Ø-4.69 mm
Tap drill-8.23 mm

Thread profile

millimetres unless stated
Thread profile — #1-64 UNCd 1.85d2 -4.69d3 -10.51mm60°P 0.4h3 6.18tap ⌀-8.23
#1-64 UNC — basic profile60° flank angle · Not to scale
Designation
#1-64 UNC
Thread system
UNC
Series
coarse
Flank angle
60°
Major diameter
1.85 mm / 0.07"
Pitch
0.4 mm
Threads per inch
64
Pitch diameter
-4.69 mm
Minor diameter (external)
-10.51 mm
Minor diameter (internal)
-9.06 mm
Thread depth
6.18 mm
Recommended tap drill
Ø -8.23 mm / -0.3239"

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.