Savant is a blend of atoms boom and juke urethane on an oversized core with a molded lip the oversized core not only reduces weight but increases the overall roll speed with the increased speed the molded lip plays a big role in ensuring the grip characteristics remainplease note this price is for a pack of 4 bearings are not includeddimensionsdiameter 59mmwidth 38mmmaterialsdurometer 88a polyurethaneadvised surfacesplastic wood slick sport court