Both of these mouthpieces are the 6 1/2 AL size. This is our most popular choice, and is a really great, medium sized mouthpiece that is quite versatile for all styles. This is also the choice of most of the band teachers we work with in Orange County.
 
The difference between these two options here are the shank size, which refers to the part of the mouthpiece that is inserted into the mouthpiece receiver. Small shank mouthpieces are the most common sold as this is what fits standard student lined instruments. Upgraded trombones and baritones may require a large shank. They are not interchangeable, but we do also sell an adaptor that works for small shanks to also play in a large shank receiver.