Fits E-sync hubs and includes pawls, springs, pawl retainer, 0.5mm freehub spacer, 1.8mm cassette spacer, and freehub seal. Compatible with Shimano HG cassettes. Not compatible with Shimano Micro Spline cassettes and not compatible with SRAM XDR or XD cassettes. Also compatible with Neo and Neo Ultimate hubs as a more durable upgrade.