I'm trying some random blades and loaded up this one today. Does anyone know what it is?
If the patent mark US3071856 was correct, then it should be an older blade. That patent was issued in 1963 and should have expired ca. 1980. Also, putting it on the blade at all suggests that it was intended for the USA market.
Doesn't that make it a bit of a puzzler? I assume the patent number might be a legacy-type thing.