These end caps fit 6-bolt E-sync hubs with 12x135mm or 12x150mm rear axle spacing and Shimano HG or SRAM XD/XDR cassettes. The non-drive side end cap includes a low-friction U-cup seal that snaps into place and stays secure even when your wheel is removed from your bike. Compatible with E-sync, Neo, and Neo Ultimate 6-bolt 135mm and 150mm hubs and Shimano HG or SRAM XD/XDR freehubs. Not compatible with any Centerlock hubs. Not compatible with 142mm, 148mm, 157mm, or single-speed E-sync and Neo hubs. Not compatible with Micro Spline freehubs. Not compatible with M-pulse hubs.