What is a long weight?

A long weight is something that an apprentice or new boy is sent to the stores to get. Eg: "go to the stores and get me a long weight for this job" The apprentice dutifully goes to the store-man and asks for long weight where upon the store-man goes away as if to get it returning much later and asks the apprentice "was that a long enough wait?" In other Words it is a prank traditionally played on the new and inexperienced employee !

See also: "go and get me a bag of sparks for the grinder" where the apprentice is given an empty but inflated paper bag by the store-man.