A unique aspect of Shaker chair design was the occasional inclusion of ‘tilts’ in the rear two legs, the structure of which is akin to a ball-and-socket joint. The base of each back leg was hollowed out and a wooden ball with a flat base was inserted and secured with a leather strap. This mechanism allowed the sitter to tilt back in the chair with the rear feet remaining flat and therefore not damaging the base of the chair or the floor. The use of ‘tilts’ in Shaker chairs was introduced as early as 1819.