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) The AX shank is a 3/100 taper and is compatible with Alexander and Yamaha double taper shanks. Used for about six months! Purchased two 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 can produce a bright tone while playing low notes. Thank you for your consideration!