ST Racing Concepts ST4142XS 3-Piece Shoes/Flywheel for Revo (Silver) CNC machined aluminum flywheel (40mm size for bump start use) CNC machined aluminum clutch shoes for precise clutch engagement and feel, special clutch nut for 3-shoe setup and matching tension clutch springs Complete clutch upgrade will enhance the performance of your Revo 3.3 while also allowing the use of bump start to start your engine