Thanks. I am guilty of skimming. When I was looking at patents assigned to Wilton in the same timeframe as the production of the Flip-Grip, I saw that patent and another (3768797 / 1973, pertaining to the versatile jaws), on both DATAMP and vintagemachinery.org, but neither the titles (both filed as "Vise Assembly") or the drawings screamed Flip-Grip to me. They are actually both related.
Have you seen any examples with the patent forged in?
I'm not sure what sequence the finishes came, soylent green or red, but all the examples I have found have the forged-in "PAT. PEND." marking.
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When searching for other examples of the Wilton "Flip-Grip", I found a completely different Wilton vise, with a completely different tilting feature - a single long pin running the entire length of the body, allowing the entire vise to tilt on any angle, anywhere from, oh, say, 10* to 170*. Example
here. For future reference for anyone else who might be equally confussed, this is the Flip-Grip II. Introduced in 1980, as far as I can tell (does not appear in 1978 or 1979 catalogs).