Charles F. Coates obtained a patent June 17, 1952, Patent Number 2,600,617. I believe this is the patent that Williams manufactured their adjustable crows foot wrench under. They made a 3/8 and a 1/2 inch version. These go for pretty good money on eBay. I have one of each but mine have been marked by a previous owner. I have seen the Snap On version before and there is another version being sold in the UK but I'm not sure who the manufacture is. Just one of those things that you have to add to the collection because it is out of the ordinary.