I'm working on a 1939 Firestone Twin Flex, and while servicing the wheelset, I noticed that the front hub is a New Departure model WL. Is that correct? I've always been under the impression, that those hubs were post war. When did the WL get introduced? I've also been wondering about the timeline of the brakearm script on the Model D hub. The first generation had a small arm with script> New Departure Model D The second had a small arm with script> New Departure Brake The third had a large arm with script> New Departure Brake The forth had a large arm with script> New Departure What years were each of these variations introduced?