This is an 11lb. counterweight for you folks that have your mount loaded down for astrophotography or such. I know it will work on CG-4 or CG-5 mounts, but I'm sure there are many more. The counterweight has an I.D. of 20mm, so if your shaft has an O.D. of 20mm it's a match. It has a plastic tipped set screw for no mar use. The counterweight shows no sign of use. It will be $40 with shipping included.