Paxman 5A Cup Paxman 5X Rim (Rim cannot be replaced) Inner Diameter: 17.5 Throat Diameter: 4.5 Rim Width: 3.75 Shank: American This is a rim-changeable mouthpiece, but the rim is stuck and cannot be replaced. A repair shop might be able to fix the stuck rim, but we cannot guarantee it, so please be aware of this.