Thank you for viewing! [Product Name] willie's French Horn Standard AST AX [Details] This is a French horn mouthpiece. AST (Inner diameter 17.45mm / Throat diameter 4.9mm / U cup) AX shank is 3/100 taper, compatible with Alexander and Yamaha double taper shanks. Used for about half a year! Purchased 2 years ago! Because the throat is deep, it's very easy to produce low notes, and I used it for the lower register on an Alexander instrument. It's rare for a mouthpiece for the lower register, but it's easy to make a sound and you can produce a bright sound while playing low notes. Thank you for your consideration!