This is a set of aluminum clutch shoes, and come stock in the Mugen MBX5 and MBX6 buggy kits. These aluminum shoes tend to hit harder than the black or white shoes with little slip. These shoes would be good for situations when the traction is very high. The most common spring used with the aluminum shoes is the 1.0mm springs. Note that aluminum shoes require a decent amount of maintenance, as they will tend to 'melt' so you need to clean up the edges of the shoes with an Exacto knife on a regular basis to make sure the shoes don't get caught on the flywheel.