Abstract: An expansion shell is formed from a single piece of sheet metal consisting of two spade-shaped leaves connected by a narrow portion which becomes the bail. The leaves are corrugated along their transverse axes so as to form a series of undulations of increasing amplitude and the leaves are formed into semi-cylinders. The corrugated semi-cylindrical leaves are centrally slotted along their longitudinal axes so as to form four leaf segments. The corrugated leaf segments are then compressed along their longitudinal axes so as to cause the undulations to form a tapered pleated metal fold, wherein the crests of the undulations become semi-cylindrical ridges capable of gripping the rock formation.