Keyhole mount clip for rectangular tubing

This is an adapter to hang my mailbox from that clips on to my porch railing. The railing is a rectangular tube 38.5mm wide by 19.6mm thick. The mailbox has a keyhole-style hanger with a large diameter of just over 8mm and a small diameter just over 4mm. The back panel of the mailbox is recessed about 13mm from the back edges of the frame and lid.

I printed a pair of adapters and clipped them onto my porch railing, then hung the mailbox from them. It probably would have been better to model this as two parts and to have the pegs screw in to the clip (or just be standoffs with holes in to accept a real screw) but this worked well enough.

This is pretty specific to my situation, but if it helps someone out I'm glad to help.