All performance machine discs use a stainless steel outer band PM uses a high grade 420 stainless that will not gaul or squeal like lesser quality discs The latest version of MP outer bands can be removed and replaced once worn All PM discs use a machined aluminum carrier The Carrier is matched to its respective wheel and will have a pattern specific to the front or rear; Note: Will not work on stock Harley-Davidson wheels, only fits Performance Machine wheels.