The horizontal supporting bands onto which quires are sewn at the spine to form the book. Cords are generally bands of leather (or sometimes other materials such as hemp) and could appear in single or double form; in the latter, the cords are split along most of their length to allow a double, figure-eight sewing around them for additional strength. The ends of the cords are then threaded into the boards (see Channeling and Pegging) and the structure covered. The cords appear as raised bands when seen through the covering of the spine, but beginning in the later sixteenth century could fit into grooves 'sawn-in' to the quire to produce a flatter spine. See also Sewing on supports and Sewing stations.