A Pit Prop
is a length of lumber used to prop up the roofs of tunnels in coal mines
. The term is used in Britain. Canada
traditionally supplied pit props to the British market. As coal mining declined in importance and metal supports were used, the term became infrequently used.
Though it was merely a log cut to a particular length, it was classified as a finished product and so got around the extra tariffs on the export of raw lumber.
Because of the large quantities exported, it was felt that many ended up in British pulp mills.