Arch-keystone system

摘要

The system comprises stones, each having two or more sides with an inner curve and two or more with an outer one. They are joined by straight ones. The stones are generally rectangular or square, or of any special shape. The keystones can have distance-pieces (8) on them so as to a constant seam width, together with a peripheral chamfer at the top. They can also have tongue-and-groove joints, the tongue extending from the bottom surface to the middle and then sloping to join the main body, loads being transmitted via the sloping faces.