Help mounting a 300mm Ronar

Hi All,

Just got a 300mm ronar off ebay, looks like this one 280016841797, and am not sure how to mount it. It has one flange, no holes for screws like others I've seen, and the flange hasn't budged to my careful attempts at unscrewing it. So, firstly, does it unscrew? Secondly, what's the best way to unscrew it if it does? Thirdly, if it doesn't, how do I mount it? The good part is the glass is intact. It says stat-king on the barrel, FWIW. Thanks a lot for any help,

GB

a picture of the rear portion of the lens would be of great help in trying to assist you.