5/16" push-button compression bolt (a.k.a. "buttonhead" or "split-shaft"). Removed along with 2 others from atop "the Nose" at Gibraltar Rock in Santa Barbara. Only 1-1/2 inches of compression held this bolt in the wall. It was removed by driving a piton under the hanger and only required a couple of easy taps on the piton. It is amazing that these three did not fail when used to configure a top-rope anchor. All three bolt holes were ovular in shape--proving that the rock itself was not hard enough to create even slight compression of the bolt.