Like Leon mentioned, many strip card sets, including W513, appear in a variety of card stocks. Check out these three examples of Rube Benton. Not only do the cards have some color variation on the fronts, but they also have 3 different types of back paper. The one in the center is maybe slightly thicker, using the old sliding a finger over the back side test while lying flat, but definitely nowhere close to twice as thick.
Brian (don't forget to update your Kraken number!)
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