I was going through my collection of Thompson mags and one didn't feel just right. It seemed as though a Thompson mag had shrunk. Looking closer the manufacturer turned out to be United Defense Supply. I have only seen maybe two um42s that I remember. I have no idea when or where it came from as I had a habit of picking up Thompson mags at gun shows when I found a deal. Could someone please give me an idea on it's value. It's next to nos. Thanks for sharing any information you can.