UNCcoarse60° flank
#12-24 UNC Thread Dimensions
#12-24 UNC is a coarse pitch UNC thread. There are 24 threads per inch, giving a pitch of 1.06 mm. The recommended tap drill leaves roughly 75% thread engagement.
Nominal Ø5.49 mm
Pitch1.06 mm
Threads per inch24
Pitch Ø-11.97 mm
Tap drill-21.39 mm
Thread profile
millimetres unless stated- Designation
- #12-24 UNC
- Thread system
- UNC
- Series
- coarse
- Flank angle
- 60°
- Major diameter
- 5.49 mm / 0.22"
- Pitch
- 1.06 mm
- Threads per inch
- 24
- Pitch diameter
- -11.97 mm
- Minor diameter (external)
- -27.49 mm
- Minor diameter (internal)
- -23.61 mm
- Thread depth
- 16.49 mm
- Recommended tap drill
- Ø -21.39 mm / -0.8423"
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.