I've used them as thread chasers on very old bolts from horse machinery and wagons. The top one, if you look close was made by Butterfield & Co. Derbyline Vt. and the bottom line stamped in the same font, is Rock Island, F.A., which I take to mean the Federal Arsenal at Rock Island, Illinois. I picked these up mainly to duplicate the odd threads sometimes used in the past, and as a sideline to my blacksmithing. I have always enjoyed Roys work too.