EngiRef / UNC Bolt Specification
1/4-20
1/4-20 coarse UNC bolt: 20 threads per inch, 6.35 mm major diameter. Tensile stress area 20.5 mm² per ASME B1.1. Takes a 11.11 mm wrench. Free imperial…
Specification
- Size
- 1/4-20
- Threads per inch (TPI)
- 20
- Major diameter D (mm)
- 6.35
- Minor diameter D₁ (mm, internal thread)
- 4.98
- Tensile stress area (mm²)
- 20.5
- Wrench size (mm)
- 11.11
Tensile stress area follows ASME B1.1, At = 0.7854(D − 0.9743/n)² in², converted at 645.16 mm²/in². Verify against the current standard and the fastener manufacturer's data before safety-critical design.