These mouthpieces have the same design as the standard C series mouthpieces but in a 17.5mm cup diameter. They are also available in different cup sizes. The M cup is a medium deep cup used on the original C12 mouthpiece. The S cup is a shallow cup originally used on the C15 mouthpiece. So a CA8 will have a 17.5mm inner diameter, a #8 bore and a deep cup. A CMA10 will have a 17.5mm inner diameter, a medium deep cup, and a #10 bore and so on. We will be stocking the 8,10 and 12 sizes in medium and stock cups but we'll be happy to order any size that you require.