Plastic Kitchen Shelf support brackets. It's cold and windy, why go to the Hardware store for a pack of 12 shelf supports at an extortionate price when I only need one and I have a 3D printer.
Printed with 20% infill 3 shells (because I forgot to change from my last build) and a support for the sticky out bit that fits into the hole in the wood side panel.

Approx 7 mm long tube, radius of 2.6 mm with a block on the end 12 mm x 12mm x 12 mm.

Designed in FreeCAD.