New style nickel-plated solid brass counterweight used on post July 2015 manufactured King trombones. 1-1/2 inches in diameter. Built like the old counterweight used on the 1960's and earlier models. Threaded design mounts to any King trombone main tuning slide cross brace, including those models with the sticker-on-nickel counterweight. This is a classy addition to your King, and makes your horn better look the part, and less like a student model. -cdp