Three-legged Lewis
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A Three-Legged Lewis , also known as a Dovetailed Lewis fits into a dovetailed seating in the top of a building stone, allowing it to be lifted by a crane or winch into position in a masonry structure.
It is made from three pieces of rectangular-section 13 mm-thick steel (legs) held together with a shackle, allowing connection to a lifting hook. The middle leg is square throughout its length. The outer legs are thinner at the top, flaring towards the bottom. Held together, the three legs form a dovetail shape. The Lewis hole seating is undercut (similar to a Chain-Linked Lewis hole) to match its profile.
[edit] Inserting a Three-Legged Lewis
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.
This type of Lewis is the safest to use because it relies on its dovetailed shape for security instead of friction alone, however the seating is time-consuming to prepare.
