Fig. 86
Fig. 87
Fig. 88
Fig. 89
The first class is the inferior, as, when fitted into the stone, any jerk of the supporting chain would act at the points A as a blow on the stone, thus increasing any tendency to fracture.
The hole for the reception of the lewis is cut, so that a line down its centre would run across the centre of gravity of the stone; and it is made as deep as may be required by the weight and hardness of the material.