The closer a mouthpiece comes to fitting your personal physiology, the greater the results you can expect to achieve. If you have thicker, fleshier lips, the larger 17.5mm will give you more of the room you've been looking for. All Stork CMA series French Horn mouthpieces have a medium deep cup depth and an inner diameter of 17.5mm. They are available in 6, 8, 10, 12, 15 and 18 bore sizes.