Bolts installed at intersections to measure roof sag. A sag bolt is a 12-ft (3.5-m) unit put in without a bearing plate. It is securely anchored in the 12-ft horizon with the aid of a heavy nut, and extends about 2 in (5 cm) from the hole. Three 1/2-in (1.3-cm) strips of colored pressure-sensitive tape are wrapped around the extending section of the bolt, beginning with green at the roof line, then yellow and red. The color bands provide a simple, economical means of detecting roof sag at a glance.