What is a snare throw off?

A snare throw off works with the snare butt to tension the snare wires on the bottom head of a snare drum. The throw off includes a system for engaging and disengaging the snare wires onto and off of the bottom resonant head. It also usually includes a tensioning system for tightening or loosening the snare wires, which will typically be attached using a screw rod with a drum key head.