Lou, the one handle "cams" against the moveable jaw, which has a pivot hinge further back on the tool. Hmmm, guess I didn't explain that very well but bottom line you move the handle a long ways and the jaw doesn't move very far, hence compound leverage.
Al, the jaws stay "mostly" parallel to each other throughout their full range.
Lyndon, I did not know there were two sizes. Mine measure 8 inches long. Do you know if the other size is larger, or smaller?
Mike, agreed, a very tight grip.
Evil, my Penens has the exact same handle pattern as the Proto and the P&C pictured on the Alloy Artifacts page I linked to in my first post.