This high quality accessory is the compression spring for 50cc, 125cc, and 150cc GY6 Engines from NCY These springs are available in a 1500 rpm ratingDescription This high quality accessory is the compression spring for 50cc, 125cc, and 150cc GY6 Engines from NCY. These springs are available in a 1500 rpm rating.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. This NCY 1500, rpm compression springs are specifically for the GY6.Let Monster Scooter Parts be your source for NCY scooter parts and accessories. WARNING California Residents: Proposition 65 Warning Specifications Inner diameter: 48.5 mm Spring height: 154 mm