ROLL LINE DEVIL 57mm Professional Injection FreeStyle Wheels Part Number: STRUDEDiameter: 57mmCompound: A NEW Roll-Line patented-Mixed Compound Elastomeric Formula The Roll-Line DEVIL 57mm Professional FreeStyle Wheels represent completely NEW design in the Patented Mixed Compound Elastomeric Formula and the start of a whole new class of Wheels. This very high quality wheel, is designed to be used on many types of extremely slippery skating surfaces including standard wood floors coated with plastic or poly urethane, but also unusual surfaces like, tile type basketball and volleyball courts, tennis courts (Indoor or outdoor), and concrete or terrazzo surfaces that are more common around the World. The DEVIL 57mm Professional FreeStyle Wheels are used a great deal internationally, where there are few indoor skating centers like there are in the USA. The Roll-Line Devil 57mm Professional FreeStyle Wheels utilize a stiff Delrin hub which is Strong, Light, and with Close Tolerances for Roundness, Trueness, and for the Cage where the Bearings and Spacers are mounted. The Roll-Line Tread is a NEW Patented Injection Molded secret Mix of Elastomeric Materials Formula, which provides ultra-strong Grip, even landing on the outer edge of the wheel, while providing great ROLL with a “Noiseless Effect”. New in 2023: expanded durometer range to replace the discontinued Fluido wheels in seven hardnesses to match any surface. The Roll-Line DEVIL 57mm Professional FreeStyle Wheels have a little more feeling of spring or bounce as they have a higher REBOUND than most other Roll-Line Thermo-Plastiche and Urethane wheels (except the Helium Wheels). This REBOUND creates a feeling of smoothness to the roll on the floor. The Roll-Line DEVIL 57mm Professional FreeStyle Wheels has a small profile width. The tread color identifies which hardness the wheels are.36D = Ivory39D = Aqua42D = Light Blue 45D = Pink 47D = Ocean Blue 49D = Grey 53D = Cream