Definition of roof bolt

i. A long steel bolt inserted into walls or roof of underground excavations to strengthen the pinning of rock strata. It is inserted in a drilled hole and anchored by means of a mechanical expansion shell that grips the surrounding rock at about 4 ft (1 m) spacing and pins steel beams to the roof.

ii. Synonym of: rock bolt

iii. Current roof bolting consists of steel rods, 5/8 to 1 in (2 to 2.5 cm) or more in diameter and 3 to 8 ft (1 to 2.5 m) in length, anchored by a mechanical expansion shell, resin grout, or a combination of both. Grouted bolts may be fully or partially grouted. A steel plate, sometimes in combination with wooden headers or steel straps, fits tightly between the bolthead and mine roof or rib.