Greg Black Bass Trombone Mouthpiece 1/2G Regular Rim Diameter: 29.31mm Throat: 8.02mm This is a 1/2G size, which falls between 1G and 0G, not 1-1/2G. Although it's difficult to see in the image, the Greg Black 1/2G has two slight indentations inside the cup from the number stamping. Please note that these are not dents from use. It is presumed that these indentations were present before the plating process. This symptom often occurs with the 1/2G model. It is believed to be caused by the cup depth, blank, and the slightly different stamping location compared to the 1G and 0G models.