Full definition
The diameter measured at the outermost edge (top of the groove lands) of a V-belt pulley, also known as the outer or external diameter (OD). This is the dimension most easily measured with calipers and is the standard commercial catalog designation. The OD is always larger than the pitch diameter because the belt sits inside the groove. The difference between OD and pitch diameter depends on the belt profile: SPA ~4 mm, SPB ~5 mm, SPC ~8 mm, A ~5 mm, B ~6.5 mm, C ~9 mm. For timing pulleys, the OD is the diameter over the tooth tips. When replacing pulleys, always verify that the pitch diameter matches the drive design requirements, not just the OD. Standard OD series for V-belt pulleys: from 50 mm to 1,000+ mm in standardized increments per ISO 4183 and DIN 2211. Material and groove count are also specified alongside OD when ordering.