Dummy Break Disc for YD-2 Series. They are molded together with the hex hubs of wheels, and come with 2 of each of the 3 wheel hubs are 0.2 inches (5.5 mm), 0.2 inches (6.5 mm), 0.3 inches (8.0 mm). Can be used alone, of course, but when combined with Dummy Break Caliper (Y2-415BCP) for a more realistic look.