Small shank Thin tube Grantz glantz This is a Grantz thin tube mouthpiece. It's a two-piece type with a cup and backbore. The cup is stamped with 6.0 3 The backbore is stamped with 2 The throat is 6.0mm, and the inner rim diameter is probably around 25mm. The playing feel is between a 6-1/2 and a 6-3/4.