A Lewis is one of a category of lifting devices used by stonemasons to lift large stones into place with a crane, chain block, or winch. It is inserted into a specially prepared hole, or seating, in the top of a stone, preferably above its centre of mass. A three-legged Lewis used throughout the Bath stone quarries, fits into a dovetailed seating in the top of a block of stone. It is made from three pieces of rectangular-section steel 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 to match its profile. These were also used horizontally for anchor points when pulling blocks out of the headings and onto wagons for transport. Also in the early use of cranes underground, these were used in sets of three to keep the crane upright before the use of chogs in the ceilings.

The first outer leg is inserted into the Lewis hole, followed by the second outer leg. The inner (parallel) leg is inserted last, pushing the outer legs into contact with the inside of the Lewis hole. The shackle is unbolted, placed over the legs, and the bolt fastened through both the shackle eyes and the eye in the top of each leg. A crane hook is connected to the shackle for lifting.

The name ‘lewis’ was supposedly the name given by a French architect who named it after his King, Louis XIV. He called it Louis which the English miners corrupted to ‘lewis’