iOptron's 11 lb Counterweight is designed to provide additional counterbalance for the iEQ45/Pro and CEM60/EC mounts, or any other mount with a counterweight shaft outside diameter of less than 1.11" and the carrying capacity to handle it. The weight uses a brass compression to provide a more secure locking method through distributed surface contact to ensure it won't slip or shift on the counterweight shaft, unlike a traditional single-point-of-contact locking screw and a pin.