J&H designed the Thumby to allow the player more room and flexibility for the placement of the thumb, along with a shape and material that are a bit more comfortable than metal.
 
They come in a small size that fits older stationary style thumb rests and a large size that fits newer adjustable type thumb rests like you'd find on upper line Buffet, Selmer, Yamaha, etc.
 
If you have any questions about the fit of these on your horn, or anything else, please let us know!