Fits E-sync hubs and includes pawls, springs, pawl retainer, 0.5mm freehub spacer, 1.8mm cassette spacer, and freehub seal. Bearings are pre-installed. Compatible with SRAM XDR style cassettes. SRAM XD cassettes are compatible when used in conjunction with the included spacer. Not compatible with any Shimano cassettes. Also compatible with Neo and Neo Ultimate hubs as a more durable upgrade.