Clip for thick materials

A clip to grab materials 20mm thick or thicker.  In the picture 4 clips are helping me make a cyanotype print of some plants.

Link to a FreeCAD model you can modify. https://www.dropbox.com/s/43l148zld7we8ju/clip%202.FCStd.zip?dl=0Look towards the last two constraints on the sketch to mod this file easily.

I printed this in solid PETG to be tough but flexible.