The helix lives within the secondary clutch. The helix helps apply pressure to the CVT drive belt. There are two types of helixes, straight and progressive. Straight helixes will have the same angle cut the whole duration. A progressive helix with have two different cuts for different shift points. Different helixes with more aggressive or less aggressive angles can adjust the pressure on the belt and shift points. If you get too aggressive with the helix angle, and don't adjust the secondary spring you will cause belt slip. If your rpms are too low, a shallower range helix and/or stiffer secondary spring will raise rpm. This will also provide more squeeze on the belt which is useful if you are experiencing belt slip. Conversely, if your rpms are too high, a steeper range helix and/or softer secondary spring will lower rpm.