These weights add 50 grams of mass to the valve cluster, resulting in a more focused and denser sound. They are particularly effective on Schmid horns because the instruments themselves are so light. (Some players even order the double horn with stopping valve to add mass.) They screw onto the top of the casing and the cap is screwed on the top. Valve casing weights are usually used on the 3rd or 4th valve, or both.