Gold plated. Same cup diameter and throat size as the standard 4 (25.90mm diameter with 0.280" throat), but with less overall cup volume. The 4M (also known as the 4GM) is great for the tenor trombonist that wants the room of a larger mouthpiece withouta huge cup volume. A full natural sound is achieved in all registers with the balance found in the Griego Mouthpiece design. Traditional "New York" style exterior is similar in appearance to Bach models, but slightly heavier, with the weight distributedevenly around the bottom of the cup.