Thread Size Converter
Convert between metric thread pitch (mm) and imperial TPI (threads per inch) for bolts and screws.
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Quick Reference
M6 = 1.0 mm pitch = 25.4 TPI
M8 = 1.25 mm pitch = 20.3 TPI
1/4"-20 = 20 TPI = 1.27 mm pitch
1/2"-13 = 13 TPI = 1.95 mm pitch
M8 = 1.25 mm pitch = 20.3 TPI
1/4"-20 = 20 TPI = 1.27 mm pitch
1/2"-13 = 13 TPI = 1.95 mm pitch
Thread pitch and TPI are two ways to describe thread spacing.
The conversion:
- TPI = 25.4 / pitch (mm)
- Pitch (mm) = 25.4 / TPI
Common metric threads:
- M3: 0.5 mm pitch (50.8 TPI)
- M4: 0.7 mm pitch (36.3 TPI)
- M5: 0.8 mm pitch (31.75 TPI)
- M6: 1.0 mm pitch (25.4 TPI)
- M8: 1.25 mm pitch (20.3 TPI)
- M10: 1.5 mm pitch (16.9 TPI)
- M12: 1.75 mm pitch (14.5 TPI)
Common imperial threads (UNC):
- 1/4"-20: 20 TPI (1.27 mm pitch)
- 5/16"-18: 18 TPI (1.41 mm pitch)
- 3/8"-16: 16 TPI (1.59 mm pitch)
- 1/2"-13: 13 TPI (1.95 mm pitch)
- 5/8"-11: 11 TPI (2.31 mm pitch)
- 3/4"-10: 10 TPI (2.54 mm pitch)