The line is used, between two corners, to control the gauge and face alignment of each course as the wall is built. The hardened steel pins which are about 175mm long are formed in two parts. A 75mm shank is made with a large head, to hold the wound line, and joins a 100mm thin blade for inserting into cross-joints. Line is wound clockwise on one pin and anti-clockwise on the other and fitted to the top face of the course.