The makers say
We have redesigned the professional 600 series trombones! The line includes four models, all of which are perfect for professional trombone players as well as college level musicians. All new models feature a 2-piece yellow-brass bell, a slide in Xeno quality and will include a mouthpiece (size 48). A lightweight slide for these models is available optionally.
YSL 620, YSL 620L L- Bore F- attachment with mechanical linkage Replaces the models YSL 682G, YSL 682GL, YSL 648R