Lewis (lifting appliance)

A lewis (sometimes called a lewisson) 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, directly above its centre of mass. It works by applying principles of the lever and utilises the weight of the stone to act on the long lever-arms which in turn results in a very high reaction force and friction where the short lever-arms make contact with the stone inside the hole and thereby prevents slipping.