A tinker traveled from town to town repairing tin pots, kettles, and pans and got his name from the noise he made while working.
His equipment included clay from which he made a mold to hold melted solder for refastening handles and joints.
He called this mold a “dam,” and because it was only good for one pot, the tinker tossed it when the job was done.
That’s how a tinker’s dam became synonymous with worthless.
