This is a vintage hard rubber Otto Link Reso Chamber mouthpiece for the alto sax, serial number 3184. This piece, stamped a 5, is in excellent original condition and measures .065". It is in outstanding shape, with no major wear of note. There is some minor scuffing on the bite plate, and that's it. Even most of the white lettering remains intact with no fading. Finding these great vintage pieces in this kind of condition is almost unheard of.