A historic mill worker responsible for grabbing hot sheet metal as it exited the rolls, folding it over on itself, and feeding it back into the mill. This doubling process allowed the mill to produce thinner gauges of sheet iron or tinplate than a single pass could achieve. The job required immense stamina and precise timing to handle the red-hot metal safely.
Heard on the job
My grandfather started in the tinplate works as a doubler, folding the hot sheets with heavy tongs.