This is remix of @SchmidtN great idea and design for a modular work holder for the Shapeoko 2 CNC machine. The slots are 1.5" on center and sized for a 1/4-20 bolt. It's best to use a 1/4-20 washer between the bolt head and clamp.
There is a great deal of pressure on the face of these clamps when the bolts are torqued down. High infill will help keep them from collapsing under the pressure.
Added gripping option
I also glued craft foam to the vertical face of the 90 degree "L". This allows a soft jaw of sorts and increases grip on the part being cut.