When was it? Zebco Patent Pending Tulsa, OK reel

My grandfather worked for the Federal Government making sure that contracts for equipment, including quality assurance, packaging, etc. was honored. I guess he did some work with the Zero Hour Bomb Co. and was also an avid fisherman. This reel has made its way into my possession and I'm interested in the history. The first prototypes of Zebco fishing reels were made in 1947. But Zebco didn't move to Tulsa until the 50's. So I'm not really sure when this would have been manufactured.