This is a B♭ clarinet mouthpiece. It's a Vandoren BD5D model, originally designed for reformed Boehm clarinets, but it has been adjusted to be used with French clarinets. It can be used with instruments from Selmer, Yamaha, and Buffet Crampon, etc. It might be a good choice for those who play French clarinets but prefer the sound of German or Viennese clarinets. It has a very good blowing feel. I used it for about 4 months.