UNFfine60° flank
7/8-14 UNF Thread Dimensions
7/8-14 UNF is a fine pitch UNF thread. There are 14 threads per inch, giving a pitch of 1.81 mm. The recommended tap drill leaves roughly 75% thread engagement.
Nominal Ø22.22 mm
Pitch1.81 mm
Threads per inch14
Pitch Ø-7.71 mm
Tap drill-23.86 mm
Thread profile
millimetres unless stated- Designation
- 7/8-14 UNF
- Thread system
- UNF
- Series
- fine
- Flank angle
- 60°
- Major diameter
- 22.22 mm / 0.88"
- Pitch
- 1.81 mm
- Threads per inch
- 14
- Pitch diameter
- -7.71 mm
- Minor diameter (external)
- -34.31 mm
- Minor diameter (internal)
- -27.66 mm
- Thread depth
- 28.27 mm
- Recommended tap drill
- Ø -23.86 mm / -0.9393"
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.