After being sick of seeing my tapestries and flags sitting around and not hanging on my wall, and not wanting to search out existing solutions, I designed these. The hook holes are 12.5mm in diameter and the whole piece is about 55mm in length. The arms take some force to open, but I can guarantee that whatever gets put between those teeth will not be coming out.

PrusaSlicer suggested using a brim, 2mm worked for me. 15% infill.