We try to steer people to the books about Griswold and Wagner. We refer to them as the Red, Blue, and Yellow Schiffer books. In those books, there is an example of the Telflon coated pan the Wagner foundry made after they were bought out in 1959. These skillets, as well as yours, only had bottom size markings in inches at that time (early 1960's). "Made in USA" was not yet prevalent on all domestic cast iron cookware. The Asian invasion wasn't really rolling until the 1970's, and that drove US foundries to start consistently mark their products. But everything hit the fan in the 1970's: recession bleeding over at the end of the 1960's, oil embargo, inflation, low cost import cast iron, and the eventual no more spare parts for the old cast iron polishing machines.Earlier unmarked Wagner also does not have the size written in inches on the bottom, only the whole number is indicated, i.e., #3 (and perhaps an inventory number), not 6 1/2 inch skillet. That type of size indication appears to have started with BSR's Century Line of cookware, and Wagner picked up on that starting in the 1960's.