Okay I Googled this and was disappointed by the answer. To start this, the engineering staff here was looking at a dial caliper and talking about the upper jaws to make an inside measurement. I asked what was the actual technical name for them and no-one knew. The answer from Googling was just "upper jaws". Now on such an important device that hangs around very technical, often over educated people, surely they have a more sophisticated name than just "jaws", don't they? That sounds like a term a mechanic hung on them.
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