You know many of the antique tools I have are almost duplicates. I guess it is whoever gets to the patent office tthe first, even tho they have their own patents. Take the standup stretcher and tacker, the Belvidere, there are at least 5 different tools that are almost identical and all with patents. Some are just an improvement of the other. But then again they didn't have computers back in the 1800's to run a comparison check.