Basics of Hexes
Hexes are a type of Passive Protection that can cover medium to large sized cracks. Most hex placements are only appropriate for one direction of pull (normally down). Hexes are also known as Cow Bells and Hexcentrics.

Many companies are experimenting with the shape and dimensions of hexes right now (Metolius and Wild Country are bringing out rounded hexes). The unique shapes may be better for your climbing locations so ask locals about the nature of the rock before investing.
Full Article