AR Resonance trumpet/cornet mouthpieces. Both are made of brass with silver plating. ◯ Top Model Number: MLB 40 Rim Size: Slightly smaller than Bach 1-1/2, the rim is semi-round and feels slightly thicker. Cup Size: B (slightly deep) Throat: 4mm (equivalent to #21) ◯ Under Model Number: PS S 40 Bore Size: S (relatively tight) Throat: 4mm (equivalent to #21) ※ The bore axis appears to be misaligned when looking at the shank end, but it doesn't feel too out of place (in my personal opinion).