If your BCD currently lacks a sternum strap and you want the benefit of using one, or you want a spare backup strap, then this easy to install strap assembly is what you're looking for. A sternum strap increases the stability of your BCD/cylinder system by preventing the shifting of the BCD when you're swimming on your side or turning on a dive. It also keeps the shoulder harness close to your center of gravity, which also increases BCD comfort.