The top bolt snap is a safety clip, a redundant point of attachment in addition to the bungee which wraps around the tank valve. This clip connects to the shoulder D-ring on both the left and right side of SMS harness. The lower clip is secured using the cam band and tri-glides and connects either your rails (for steel tanks) or on a sliding D-Ring (for aluminum tanks, sliding D-Rings not included) on your waist strap.
!