This high quality accessory is the compression spring for 50cc, 125cc, and 150cc GY6 Engines from NCY These springs are available in your choice of three ratingsDescription This high quality accessory is the compression spring for 50cc, 125cc, and 150cc GY6 Engines from NCY. These springs are available in your choice of three ratings.Compression springs do a couple of things. First they supply the pressure to engage the belt. They also determine the rate at which the CVT transmission changes from low to high gear. A 1000 rpm spring will go into a higher gear than a 2000 rpm spring.Let Monster Scooter Parts be your source for NCY scooter parts and accessories. ? WARNING California Residents: Proposition 65 Warning Specifications Wire diameter: 4.0 mm Inner diameter: 49.0 mm Length: 106.0 mm