This ddrum Pro Trigger kit contains 3-Pro Tom Triggers, 1-Pro Bass Trigger, And 1-Dual Zone Snare trigger. The ddrum Pro Acoustic Triggers feature a very sturdy mechanical housing, an XLR jack for safe connection to the sound module, and they can be mounted anywhere around the hoop. The specially designed transducer is softly pressed against the bass drumhead. The advantages are obvious; you can change drum heads over and over without damaging the transducer, the metal casing protects the trigger from accidental drum hits and the ultra-light pressure of the transducer against the head prevents any "damping" effect.