this is a card holder I designed and sold that is easy to produce and costumize. it is generally designed for a multicolor print, or a print with a layer swap if you dont have a multicolor printer.
throwing it together is basically a matter of choosing one of the canvases (according to the card holder you desire to print) and  exrtude an svg on  to it (in solidworks you can convert a .svg file to .dxf and use that to extrude it). than you print it, and glue the 2 pieces. that simple!
reccomended print orientations for cards are shown in the photos.
on the canvases I would reccomend printing a brim, totally optional, i just really like them :)
if you need any help or tips, feel free to reach out!

p.s: the stitch card was a first iteration i used for myself, what i uploaded is a much less stupid successor