PATENT ROSTFREI Vintage 21cm Italian OTF DA automatic knife

PATENT ROSTFREI Vintage Italian OTF DA automatic knife. The knife came direct from Italy along with some New Old Stock knives from the 1970s. I believe these were made in Maniago by Rosa Uliana Primo. The knife measures 21cm open. The blade is full with factory edge and is stamped PATENT ROSTFREI and I can see the letters "RN" faintly etched on the face of the blade. I'm guessing it was originally etched ERN, but the etch has faded, or wasn't strong from the beginning. The frame appears to be non-magnetic cast and the button is also metal and pinned. The DA (double action) knife functions great with blade shooting out when you push forward on the button and closing when you pull back on the button. EX+ condition.