This is a hard stop for the Creality CR-10 Max Y axis. The hard stop is attached to the inner part of the opposite rail where the limit switch is mounted. 3 M5x25mm screws and 3 slot nuts are required to hold it in place. This will protect the endstop from damage The distance measured from the endstop body to the back of the rail is used to adjust the final placement of the hardstop.