This is the alto trombone mouthpiece (cup only) from a Slowcar, before the current model was changed. The current model is Depth 25, Bore 5.8, but this one is Depth 27. It is compatible with B rims (27mm~), so I think it can be used when switching from a bass trombone. It is recommended for those who play alto or small-bore tenor trombones. Please consider it if you are interested.