UNFfine60° flank
9/16-18 UNF Thread Dimensions
9/16-18 UNF is a fine pitch UNF thread. There are 18 threads per inch, giving a pitch of 1.41 mm. The recommended tap drill leaves roughly 75% thread engagement.
Nominal Ø14.29 mm
Pitch1.41 mm
Threads per inch18
Pitch Ø-8.99 mm
Tap drill-21.55 mm
Thread profile
millimetres unless stated- Designation
- 9/16-18 UNF
- Thread system
- UNF
- Series
- fine
- Flank angle
- 60°
- Major diameter
- 14.29 mm / 0.56"
- Pitch
- 1.41 mm
- Threads per inch
- 18
- Pitch diameter
- -8.99 mm
- Minor diameter (external)
- -29.69 mm
- Minor diameter (internal)
- -24.51 mm
- Thread depth
- 21.99 mm
- Recommended tap drill
- Ø -21.55 mm / -0.8486"
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.