The Silky 13B is a mouthpiece suitable for the side positions in wind bands and big bands. The size is about the same as a Bach 5. The cup is a gentle W cup, similar to a Bach C cup. The rim is flat and slightly thick. It has a soft feel on the mouth and a clear outer edge of the rim, making it easy to grip. The throat is close to #27 (3.66mm). It's easy to play with a deep cup equivalent to a Bach 5C. [Cup Inner Diameter] 16.76mm [Throat] 27