Not all tinkers were gypsies.
By definition, a tinker was a traveling repairman who could fix most anything on the American frontier. He could gunsmith a little, blacksmith a little, carpenter a little, sew a little, and yes a tinkers dam was a clay ridge to hold molten metal that was poured to effect a fix. Once used , it was not valuable at all, just hard clay again.
He was a jack of all trades and some times even a master of some.
In Europe they may have been predominantly Gypsies but not here.

Phelonius
BTW ever wonder about the phrase, " tinker with it?"

Phelonius,you must remember this is a very young country,sh1t even my local Pub in London was a hundred years older than the US.   Gypsies came mostly from Hungrey,we were also told that they would kidnap children if they were short of labor,I think that might be an old wives tale to keep us kids away from them.
Not long ago there was a big family of Gypsies working the San Diego area,they would sign you up for a roofing job,pay the half in advance ,and you would never see them again.
FYI  A pub is short for "Public house" even if a traveler had no money the publican was oblidged to offer some bread and cheese,and somewhere to sleep,even if it was the barn.