Bonnet

1. A covering over a mine cage, which serves as a roof to shield it from objects falling down the shaft, thereby protecting the riders. Syn: cage cover
2. A cap piece for an upright timber. Zern
3. The metal casing of a miner's flame safety lamp, with openings at the top and a hook for carrying the lamp. The bonnet protects the inner gauze from damage and from the impact of high-velocity air. See also: safety lamp
4. Syn: air dome
5. The cap over the end of a pipe. Strock, 1

Source: Dictionary of Mining, Mineral, and Related Terms