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 1000rpm spring will go into a higher gear than a 2000rpm spring.
This NCY (Blue) 1000 rpm compression spring is specifically for the stock GY6, (Yellow) 1500 rpm usually for Street and (Red) 2000 rpm for Race. SOLD EACH.
Spring I.D.: 48.5mm
Spring Height: 154mm