UNCcoarse60° flank

2-4-1/2 UNC Thread Dimensions

2-4-1/2 UNC is a coarse pitch UNC thread. There are 4.5 threads per inch, giving a pitch of 5.64 mm. The recommended tap drill leaves roughly 75% thread engagement.

Nominal Ø50.8 mm
Pitch5.64 mm
Threads per inch4.5
Pitch Ø-42.32 mm
Tap drill-92.57 mm

Thread profile

millimetres unless stated
Thread profile — 2-4-1/2 UNCd 50.8d2 -42.32d3 -125.09mm60°P 5.64h3 87.95tap ⌀-92.57
2-4-1/2 UNC — basic profile60° flank angle · Not to scale
Designation
2-4-1/2 UNC
Thread system
UNC
Series
coarse
Flank angle
60°
Major diameter
50.8 mm / 2"
Pitch
5.64 mm
Threads per inch
4.5
Pitch diameter
-42.32 mm
Minor diameter (external)
-125.09 mm
Minor diameter (internal)
-104.4 mm
Thread depth
87.95 mm
Recommended tap drill
Ø -92.57 mm / -3.6444"

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.