well first of all, go try them on, they fit completely differently, 2nd, which specific model of supercharger boots are u looking to get? The supercharger spark boot, which is something like a 102mm last generally on the wider side and also a softer boot, the supercharger ignition boot, which i think is a 100mm last and better liner stiffer than the spark, or the supercharger blower boot which comes from the doberman mold, and has a 98mm last, and is super stiff something like a 130.