Spitfire F4 Lock-In 101D Wheels 53mmDesigned to last longer, withstand more abuse and perform superior over all other wheels. The Spitfire Formula 4 Lock Ins are manufactured using a 100% pure urethane compound, Formula Four wheels out performed and resisted flat spots longer with less wear than all other wheels. With an asymmetrical shape and design featuring a conical cut profile opposite a straight edge side. The idea behind this is to give you extra scope to lock your wheels and