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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. Coal Age, 3
Source:
Dictionary of Mining, Mineral, and Related Terms
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