Unless made in US, which not many are, they are made in production quantities, with dies, in China. The vendors buy from one "People's Fender Factory". The parts are all made the same but not all the same fit. Two reasons: The users truck is screwed up, repaired, twisted, misaligned or has other Chinese parts. Second, the parts are stacked, handled, loaded, shipped, banged, thrown, stepped on a dozen times before they get to you. (8000 miles). Sometimes they fit pretty good, sometimes we have to tweak them. This is the nature of the beast. Folks think that one vendor or another has bad parts and another has good parts. It's really just your particular piece from the batch and your truck's slight problems. Nothing to do with the vendor. They come from the same place in China. Nobody knows, including the vendor, the exact thickness. The difference between 19 and 20 ga is 1 to 1.5 human hair. The Chinese thickness tolerances easily cover that range. That's why vendors don't usually advertise a thickness.
You buy them at the cheapest price, with shipping, and make them work with your American determination. The user needs to stop crying about it a "truck on" with the fix. Cut, chop and rebuild. Adapt and overcome. Listen to the Devo song.
Just remember, you only repair the bad parts, not the whole piece, whenever possible. Even if you buy a whole piece, you don't use it all. You just cut out the rusted part. You always keep good metal. You will also have less fit problems that way. You try to mount the piece after the patch is tacked into place. You use the truck to locate the patch, when possible, before tacking. You carefully measure and make profile templates before cutting out old pieces. It's an art and a mechanical engineering exercise. Wood worker guys are pretty smart with sheet metal. Sometimes you have to loosen other body parts and move them to find equilibrium. It takes awhile to learn how to weld thin metal. Another subject for a different day.
Vendors buy form different brokers, drop shippers, warehouses and each other. They would have no idea it's all from one Chinese factory. Communism allows no competition, therefore there is only one factory. China is the only country who could afford the tooling and labor for such low quantities, sell cheap, and still make a profit.
Generally speaking , you don't replace a section or part just because it's dented. Try to take out the dent(s) first.
As I said before, donor parts are another option.
