If you google the knob, there is a chart in one of the CMPicon posts that keeps popping up that provides the makers and when they are used. I don’t know how definitive or who compiled the chart but it indicates that it’s early post war. I don’t know if it’s accurate but it’s a reference point for at least debate. I don’t recall what issue it’s in I believe you can google the index of articles or download it from the GCAicon page and then based upon when you read the article you should be able to narrow down the timeframe. Good luck.