A non-existent tool that veteran carpenters send apprentices to fetch when a piece of lumber has been cut too short. The joke relies on the physical impossibility of lengthening a cut board. It serves as a rite of passage on job sites, teaching newcomers the importance of accurate measurement while providing amusement for the crew.
Heard on the job
Hey kid, you cut this casing a half inch short, so run down to the truck and grab the board stretcher.
Insider tip
If someone asks you to find the board stretcher, wire stretcher, or left-handed hammer, they are letting you know you messed up a cut.