A three-legged lewis, also known as a dovetailed lewis, St Peter's keys, or a Wilson bolt fits into a dovetailed seating in the top of a building stone. It is made from three pieces of rectangular-section -thick steel legs held together with a shackle, allowing connection to a lifting hook. The middle leg is square throughout its length, while the outer legs are thinner at the top, flaring towards the bottom. Held together, the three legs thus form a dovetail shape. The lewis hole seating is undercut (similar to a chain-linked lewis hole) to match its profile.