UNCcoarse60° flank

#4-40 UNC Thread Dimensions

#4-40 UNC is a coarse pitch UNC thread. There are 40 threads per inch, giving a pitch of 0.64 mm. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø2.84 mm
Pitch0.64 mm
Threads per inch40
Pitch Ø-7.63 mm
Tap drill-13.28 mm

Thread profile

millimetres unless stated
Thread profile — #4-40 UNCd 2.84d2 -7.63d3 -16.94mm60°P 0.64h3 9.89tap ⌀-13.28
#4-40 UNC — basic profile60° flank angle · Not to scale
Designation
#4-40 UNC
Thread system
UNC
Series
coarse
Flank angle
60°
Major diameter
2.84 mm / 0.11"
Pitch
0.64 mm
Threads per inch
40
Pitch diameter
-7.63 mm
Minor diameter (external)
-16.94 mm
Minor diameter (internal)
-14.62 mm
Thread depth
9.89 mm
Recommended tap drill
Ø -13.28 mm / -0.523"

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.