This is a 5GS large shank mouthpiece from Tilz's Spezial series. I used it for about a month after purchase, and it has been in long-term storage since then. The size is 26.0mm, which is larger than the Bach equivalent. The bore is 6.8mm, and the cup is Medium Deep. I believe this is a hard-to-find model. It is especially well-suited for modern German horns. Please take this opportunity to consider it.