toggle joint

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A joint made of two arms attached by a pivot shaped like an elbow, allowing force to be exerted at the ends of the arms as the joint is expanded.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An elbow or knee joint, consisting of two bars so connected that they may be brought quite or nearly into a straight line, and made to produce great endwise pressure when brought into this position.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a joint made by two arms attached by a pivot; used to apply pressure at the two ends by straightening the joint