A realistic dual bearing wheel which is pretty similar how skateboard wheels with bearings are made. Also these wheels are available in different hardships which is another great benefit. Y2 are a bit softer with 60D and the Y3 and new Y4 are harder with 65D. Y2 and 3 got the classic round shape and the the Y4 the new conical shapes. They fit perfectly on the Y-Trucks and on our Shop Trucks but not on BRTs for example.