This 17lb Counterweight Accessory is designed for CGEM series computerized telescopes. Use this counterweight to properly balance your CGEM telescope around the polar axis. Expertly crafted to fit the counterweight shaft of the Advanced VX, CGEM, CGEM II, CGX, CG-5, or CG-4 series equatorial mount. The counterweight slides onto the counterweight shaft and then locks into position with a heavy-duty knurled knob.