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 the 18mm size will give you more of the room you've been looking for. All Stork CB series French Horn mouthpieces have a deep cup depth and an inner diameter of 18mm. They are available in 1, 4, 6, 8, 10, 12, and15 bore sizes.