This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol6", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The clips, as shown at A, Fig. 225, are practically indispensable for lifting thin slabs of stone or ashlar. They are easily adjusted, as the hook rings can be moved along the chain. The width of the stone to be lifted should not exceed half the total length of the chain. Chain slings may also be used for the same purpose, but the thickness of the stone usually determines the mode of lifting.
Jack slinging, as at B, should only be applied to slabs over 6 inches thick, but not of less thickness, otherwise the slab would very probably break.
The figure-eight slinging (C) is, however, the better and more customary method of lifting slabs, as there is less risk of fracture.