The depth adjustment of the router was the initial use of that plates and you may see their old version at the bottom of the tool adjustment document. Adding a stuck frame to the wood-like base strengthened the plates and made them convenient for the second usage.

They also needed some holes to match their new purpose as vertical shield between the saw blade or spindle moulder head cutter and the operator. The guard is merely an assembly of the two sliding table clamps and one plate as shown above and may be arranged so that each hold-down accommodates a plate.

But that assembly quickly raised a concern as regard safety. Even locked each guard might rotate due to leverage and cause damages to the operator. The angle fixture fixed the issue and the guard incidentally transformed into a tenoning guard.