These end caps fit Centerlock E-sync hubs with 135mm or 150mm rear axle spacing. 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 Centerlock 135mm and 150mm hubs. Not compatible with any 6-bolt 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.Technology:E-sync:- E-sync hubs are built to last, including under the higher torque and weight of eBikes. A 6066 alloy shell, heat-treated steel ratchet ring, reinforced pawls, and full Enduro bearings rovide brute strength, while 8.18° engagement provides the speed.