This is a dovetail attachment that will fit to either D or V series dovetails, and is accompanied by the counterweight shaft and counterweight it permits you to attach freely. The 3.5 lbs is great for adjusting the balance of your OTA's by slight amounts, and the included CW shaft is sized perfectly to contain this Counterweight. The split clamp design grips the dovetail bar along the entire surface of the saddle and will not dent or scratch the dovetail bar. Features two large locking hand knobs for tool free operation.