[Of obscure origin.]
1. Mining. A prop used to support the coal or roof during the working of a seam.
1841. Hartshorne, Salop. Ant., Gloss., Sprags, ‘uprights,’ or pieces of wood placed upright against the sides of a coal pit, to support the ‘lids.’
1862. Chambers’s Jrnl., April, 216. They are particularly enjoined … to support the roof … with props or sprags of larch or other wood.
1881. B’ham Daily Post, 16 Feb., 7/2. The provision of the Mines Inspection Act, which requires that sprags in the workings shall be placed not farther than 5 ft. from each other.
2. A stout piece of wood used to check the revolution of a wheel (or roller), usually by inserting it between two of the spokes.
Also U.S., a rod or bar that can be dropped so as to prevent a vehicle from running backwards.
1878. F. S. Williams, Midl. Railw., 524. Having armed themselves with a piece of timber called a ‘sprag’ to be used if required as a brake, they set off.
1886. Pall Mall Gaz., 13 Sept. Sprags and other articles were thrown under the wheels without effect.
1890. ‘R. Boldrewood,’ Miner’s Right, iii. A ‘sprag,’ being a stout piece of hard wood, was inserted between the rope and the iron roller on which the rope ran.
