The most references I found to 5/16"-40 thread are "Model Engineer Thread". When I first looked at the picture I thought the die was made by "ACE" but it is actually "A & F". I did also find a reference to some form of 5/16"-40 being used for some gun cleaning rods. Is it possible that A&F = Abercrombie & Fitch? Before their more recent incarnation as a fashion store Abercrombie & Fitch sold fancy sporting goods like seriously expensive shot guns. Does anyone know of another "A&F" that made tools?