A very lightweight compact belay system carabiner from Petzl that is a pear-shaped carabiner with a keylock style gate closure for no-snag use and a screw-lock that incorporates a visual indicator band on the gate to help facilitate checking to see that the carabiner is locked.  Functional size for both clove and münter hitches.  Great for belay and anchor systems.  One of the most popular models and an industry standard in it's class. Experienced climbers all know this one by name.