This pair of front end caps is designed to fit 6-bolt E-sync OS hubs when used with 9mm quick-release axles. The included end caps are also compatible with 6-bolt Neo OS hubs. The end caps feature a low-friction U-cup seal that snaps into place and stays secure even when your wheel is removed from your bike. Fits 6-bolt E-sync OS and Neo OS hubs. Not compatible with Centerlock or non-OS versions of E-sync and Neo hubs. Not compatible with M-pulse hubs.