doubler

1. (structural engineering) A metal plate riveted or welded over a preexisting metal structural component to reinforce it and relieve the stress on the preexisting component, or to serve as a patch where part of the original structure has failed or been removed.Examples: "The mechanics fastened a doubler over the hole where the cracked section of the plane's skin had been cut out."; "The airworthiness directive called for riveting a reinforcing doubler to the wing midspar web to keep the spar from buckling under flight loads."

2. (calico printing) A blanket or felt placed between the fabric and the printing table or cylinder.

3. (metalworking) A person employed in a roller mill to fold the hot metal plates in half.