Not worth a tinker's dam
Posted by Bill Oetinger on December 30, 2003
The etymology given for this phrase indicates that it is the solder used by tinkers to mend pewter ware.
I always understood that the tinker actually had a small device among his tools that he could use to dam up molten solder and hold it in place over a repair. It was this tool that was actually a tinker's dam and not the solder itself. But I have no basis for this conjecture except having read it somewhere, years ago.