NEW OLD STOCK Bach 42BO Open Wrap Stradivarius Tenor TromboneThis is a demo model horn that has been taken to multiple trade shows. In MINT condition! The Bach 42BO Stradivarius Series F Attachment Trombone is a best seller and the ideal instrument for both advanced students and professional trombonists. An open wrap design results in fewer bends in the tubing, which creates a free blowing trombone. The 42BO with a . 547 inch bore and 8. 5 inch bell produces a large, symphonic sound with clear projection.