Wedge anchor s , also known as expansion bolt s and expansion anchor s , secure themselves using a mechanical wedging effect at the end of the fastener. There are three basic styles of wedge anchors: fully threaded, partial threaded and the full-bodied wedge anchor.  As shown in the figure, tightening the bolt results in a wedge being driven up against a sleeve. This jams the end of the bolt, and provides the strength. Many different manufacturers provide a variation on this theme, usually depending on the condition of the concrete, and the type of load. If a mechanical anchor fails, it is usually in the form of pulling out a wedge of concrete, and for this reason, proper design looks at the depth of embedment and ensures that the bolts are not spaced too closely.