[freebeard]

They only give you two of the three dimensions. Off the top of my head, auto body sheet metal is 18 to 20 gauge. I think, like wire gauges, small numbers are thicker. If the edge is rolled around a wire or rod, like a Model A fender, you could use a thinner gauge. At least fold the edge to double the thickness.

That picture shows how Weather Spotter bent the metal, but I haven't seen how they are mounted. A permanently mount may lead to disappointment alongside a dark road on a rainy night.