The Eliminator takes the place of the Selector lever on your lower receiver and allows for your MAC to shoot in full auto only. When using the CF-W Slow Fire Bolt, the selector lever is not needed because the rate of fire is slow enough that you can easily pull single burst fire. Eliminating the selector lever makes for a sleeker design and prevents any interverance from the selector lever. See the video below for assembly instructions. Note: This does not make a semi-out gun into a full auto gun.