Cornet mouthpieces come in a variety of types, and they can be easily differentiated by features such as their rim diameter, cup depth and throat. Another important difference is the sharpness of the rim. Mouthpieces for brass instruments have a numbering system, but this is not consistent across different manufacturers. Beginners typically use a mouthpiece that has a wide and rounded rim, a medium cup depth and a medium throat size.
Mouthpieces on brass instruments have common parts that affect the tone and playability of the instrument in the same way. A cornet mouthpiece has a rim around the opening, and the rim is what comes into contact with the player's lips. Just inside the rim is a cup, which has a tube attached to its bottom, in the same way the bowl of a wine glass connects to the stem. This tube is the throat, and further down, it becomes the backbore, which is the section of the mouthpiece that slides into the cornet.
The rim is one aspect that can be used to differentiate between the different types of cornet mouthpieces. The two main aspects that affect the qualities of the rim are its diameter and the edge it has. A wider rim provides the musician with better comfort and usually means that he or she will be able to play for longer, but a narrower rim gives more flexibility of tone. The edge of the rim is more comfortable when rounded but gives more precision when it is sharper.
Another key factor in telling the difference between cornet mouthpieces is the cup, which can vary in its size and depth. A small cup is easier to play and is recommended for beginners who are yet to develop their embouchure, but a larger cup provides better volume and control. A shallow cup is better for solo players, with better high-end tones, and a deep cup has the opposite effect, adding richness to the low end. A medium-depth cup is a compromise between the two.
The size of the throat is the final important difference between various types of cornet mouthpieces. A bigger throat means that more air can go through the instrument, and a smaller one means less air can go through. More air going through the instrument means that the instrument is louder and that higher notes can be slightly sharpened. A small throat and less air going through causes increased resistance during play and can flatten high-register notes.