The shelf peg can be easily printed on an FDM printer without supports and a high infill % (I might have even used 100%). I used PLA to print, but ABS or any other rigid FDM plastic should work.

I wasn't able to successfully print the clothes rod peg to be strong enough to bear sufficient load, so I just sent it out for SLS nylon printing. It might work with a really strong thermoplastic like polycarbonate or a carbon fiber filament.