Crank: 104 BCD lightweight mountain bike crank, Crank Arm Length: 170mm, Crank weight: 580g/pair. Chainring: Single speed narrow wide chainring, 104BCD, Round. Material: made of high strength aluminum alloy integrally formed, and surface is anodized and frosted, which is not fading and resist oxidation. Chainring: positive and negative arrangement makes the chain fit closely with shape, reduces chain wear, prevents the chain from falling off, and drives efficiently. Note: These crank and chainring are only suitable for single speed. Can not be used on other speed. Size Chart: Crank hole distance 170mm/6.69inch The distance between center of the hole is 104mm/4.09inch The inner diameter of the hole is 10mm Package Includes: 1 Set of Crankset