The 2mm coated aluminum spacer fits underneath the differential and slots/keys to the chassis. You could place 2 along with eachother to produce 4mm spacer. The design is manufactured such method your 2 spacers will even freeze position. Depending on the plates utilize you may have to also place out of the rear stiffener. Increasing the rollcenter will go the differential higher aswell, creating more grip and steering, but less simple to drive.