Unbeatable lasting performance SPITFIRE urethane. Fast as hell. Long lasting, abrasion resistance, smooth anti-stick slide with a controllable grip. Spitfire's premium formula four urethane in an asymmetrical shape and design featuring a conical profile opposite a straight edge side. Lock on in. Formula Four Urethane - Resists Flatspotting 54mm 99a Durometer Lock In Full Shape