Low level edge clamps

[Toolmaker51]

Nice. I kind of understand these but not entirely. Is the hole in the hex off-centre in one direction or 2? (or maybe you have a dimension sketch?). I understand the eccentric action on the bolt but what prevents it from bottoming out in the axial direction prematurely, meaning before the cam action has fully displaced the hex part? In other words the cap screw feels tight but it still hasn't fully applied lateral clamping force.

Not to usurp thehomeengineer, allow me provide an explanation. This is an effective clamp, secure enough to withstand milling and drilling; be aware burying a helical [right-hand cut, right-hand helix] cutting edge can pull the plate up. One technique uses right-hand cut with a left-hand helix to generate down force.

Off center in one axis is sufficient. Knowing the amount, it moves the hexagon laterally an equal amount on any face; one needs to pick that which locks against the part before the cam goes over center. The rail or hard stop of opposite side does the rest.
A bi-axial offcenter would produce same result, without benefit, as the cam's rotation is in the entire round bearing area. They could be round instead of hexagon; moving the same distance, but too little contact area for dependable clamp action.
A commercial version is known as Mitee-Bite