Lewis (lifting appliance)

It is inserted into a specially prepared hole, or seating, in the top of a stone, preferably 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.

The name lewis may come from the Latin levo -avi, -atum meaning to levitate or lift,[1] but the Oxford English Dictionary Online[2] states, "the formation and the phonology are not easily explained on this hypothesis", preferring "origin obscure", and speculating that the term may derive from a personal name.

Lewis holes in the uppermost masonry coursings are neatly repaired with matching indented plugs after the stone has been set in place.

When the top of the curved legs are pulled together by the rings, the bottom portions are forced into the lower part of the seating, thereby providing enough friction to lift the stone.

The two legs, semicircular in section, lie side-by-side, and fit inside a hole drilled in the stone.

It is made from three pieces of rectangular-section 13 mm (0.51 in)-thick steel legs held together with a shackle, allowing connection to a lifting hook.

This type of lewis is the safest to use because it relies on its dovetailed shape for security instead of friction alone, but the seating is time-consuming to prepare.

The external lewis was originally shaped like a pair of scissor-tongs, and swung from a treadwheel crane.

Safety chains and a support bracket allow safe lifting of large slabs.

This lifting appliance also has a safety locking device that is engaged when the gripping pads are activated by the weight of the stone.