This is a set of three replacement three shoe style 1.0mm clutch springs for Kyosho buggies, and fits the Inferno MP9/MP10 family of buggies. These are the stock springs that come in the kit, but you can fine tune the way the clutch engages by using different tension clutch springs. The bigger the spring, the stiffer it is and the later in the RPM range the clutch will engage. The smaller the spring, the softer it is and the earlier in the RPM range the clutch will engage.