FITS Beta RR 250\300 13-23 2str Beta RR 350-498 13-23 stroke The ProX alloy rear sprockets are all manufactured from high grade 7075-T6 material. The total sprocket is precision cut on fully automated CNC machines using strict tolerances which guarantees perfect fit. The sprockets come with self-cleaning mug grooves. Unlike many other rear sprockets, the specially designed mud grooves are positioned outside the pressure area of chains and sprocket to significantly increase durability.