SB1J. Pickup Mute™. Model, PM7X (for Trumpet, Cornet), PM6X (for Flugelhorn), PM5X-2 (for Trombone, Bass trombone), PM3X (for French Horn) ...
https://de.yamaha.com/de/products/musical_instruments/winds/silent_brass/silent_brass_sbj_series/specs.html