A timber frame to support the roof, sides, and sometimes the floor of mine roadways or shafts. For a mine roadway, the simplest timber set consists of a crossbar, cap, or collar supported on two upright posts or arms with round or board lagging. Such a set will resist roof pressure and moderate side pressure and is erected at intervals of from 2 to 6 ft (0.6 to 1.8 m). The timbers are about 5 to 10 in (12.7 to 25.4 cm) in diameter. In South Wales, such a timber set is known as double timber.