These are Heavy Duty stock replacement wheels for your Polaris Snowmobile. These are CNC Machined out of Billet UHMW. UHMW is a very strong and stable material, built to withstand the demands of intense snowmobiling. Our bearings are larger than stock in both outside diameter and width this provides an incredible strength. We also use larger snap-rings for durability. These are a direct replacement with no modifications required. You have the choice between 6205 and 6304 bearings. Your stock Polaris will use 6304 bearings.