The Legends Chicago Backbore: Our most open backbore, with the darkest and broadest sound. This backbore is ideal for a smoky jazz sound. But it also works well for solo and lead players who like an open blow. The shank is based upon a #5 sleeve to make sure the vast majority of horns will receive it properly. The throat is a #27. This backbore is available in two blanks. The lightweight blank is less efficient and will have a slightly tighter feel. The heavyweight blank is more efficient and will feel slightly more open.