not worth a (tinker's) damn

Worthless. The catalog of similes signifying “without worth” is seemingly endless. This one, beginning life as “a tinker’s curse,” then became a tinker’s dam, a wall of dough raised around a place where a plumber is trying to repair a hole with solder. The dough holds the solder until it hardens and then is discarded. Misspelling turned it into damn and today “tinker” is usually omitted. (However, “damn” alone was also used in the eighteenth century.) Among the hundreds of similes denoting worthlessness that are still heard today are not worth a bean (see hill of beans); not worth a fig (also see under fig); not worth a button (thirteenth century); not worth a (brass) farthing (seventeenth century); not worth the paper it’s written on (usually applied to an IOU or bad check); not worth a pin (fifteenth century); not worth a plugged nickel (plug meant a debased coin; nineteenth century); not worth the powder to blow it up (nineteenth century); not worth a rap (a counterfeit half-penny circulating in Ireland in the early eighteenth century); not worth a red cent (the cent being the smallest American coin, red because it used to be made of pure copper; nineteenth century); not worth a straw (fourteenth century). See also worth one's salt.