This is a Stork French horn mouthpiece. CMW15 It seems to be an older model, so the exact specifications are unknown, but based on how it plays, the inner rim diameter is probably around 17.5. Likely a wide rim. Cup depth is medium-deep. V-cup. This is a classic American mouthpiece from Stork. It seems to be particularly well-suited for large-bore horns and Geyer horns. Don't miss this opportunity.