Precision machined from 303 stainless steel, this 30lb Counterweight from Astro-Physics is guaranteed to be of the highest quality! Designed with a 1.875" bore size and built to be tough and sturdy as they come, this dependable counterweight is sure to meet your needs. These hefty weights slip cleanly onto the shaft of your mount and are then easily fastened in place with a large hand knob and brass pin combo that Astro-Physics ensures will not in any way mar or damage your counterweight shaft! When using counterweights in your setup, keep in mind that you can adjust the position of the weights to counterbalance varying loads. However, the addition of a guidescope, camera, and other heavy accessories may necessitate an additional counterweight. If you plan to mount your catadioptric, Newtonian or any other scope, figure that you will need a counterweight total equal to approximately 90-125% of the weight of your tube assembly and accessories (large diameter scopes require a higher percentage). The 1100GTO and 1600GTO mounts require slightly more weight than the older 900GTO and 1200GTO mounts- and this counterweight in specific is perfect for those mounts because of that fact!