used jean baptiste jbst381 student tenor trombone. perfect for beginners who want to get into band. Jean Baptiste JBST381 Student Tenor Trombone . 500" bore, the preferred size for young student. The 8" laser-fused, pluzuma welded bells for continuous even vibrations in all registers Nickel-silver seamless inner slide and brass outer slide allows for smooth slide action. Nickel-silver braces are used for added strength.