chockstone

Etymology
. The climbing sense derives from the wedges' use as artificial chockstones.

Noun

 * 1) A stone, ranging in size from a boulder to a pebble, which has become wedged in a vertical fissure or cleft.
 * 2)  A metal wedge or nut, threaded on a wire, used in rock climbing for protection by wedging it into a crack in the rock.
 * 1)  A metal wedge or nut, threaded on a wire, used in rock climbing for protection by wedging it into a crack in the rock.