This is my latest design for a smart card holder. It holds four standard ID cards.

Print it laying down with the longer, notched post toward the build plate. The material below the notch can be cut off. I print this with fairly dense support and dig it out for a decent finish on the underside.

Design file:
https://cad.onshape.com/documents/642058842d32961c74038aa2/w/237e98d4f85d460198a5d20f/e/e46e84a8b2d11a128602f670