Brass French horn parts - Material: Brass - Shape: Cylindrical - Application: French horn parts Thank you for viewing. It appears to connect an American shank to an American shank. It is unclear whether it is for pitch adjustment or for adjusting the position of the mouthpiece pipe. I only have American shank and double shank mouthpieces, so it might be a general-purpose item. It doesn't seem to be a commercially available product. It was included with a used instrument, but I didn't need it, so I thought someone else might, and I'm listing it. No returns or exchanges, please.