For Bell diameter 8 1/2" or more. With its unique shape, this all-aluminum cup mute produces a smoother, richer sound for tenor trombones. Lined with a neoprene rubber rim that eliminates vibrations, the adjustable cup will never loosen or drop off. It is easily installed by simply moving the cup up to the desired length for a tight fit. The corks may be reshaped for optimal acoustical placement.