The upgrade kit, offers stainless steel ball bearings that are of very high quality. The ball bearings can withstand extremely large loads while maintaining a perfectly smooth function. A great point to be mentioned is that the stainless steel bearings can be places on a threaded 6mm axel without sacrificing function longevity.The Rollers can function with any setup one desires. Either with hydro lubricated plugs (standard), one ball bearing and one plug per roller (for lighter head weight) or by installing full ball bearing kits for large loads.The roller head dimensions are:Width: 17mmOuter diameter: 27.5mmInner diameter: 21mmThe Stainless Steel ball bearings:Axel diameter opening: 6mm
Listing is for one ball bearing.