Make two of the provided orientation and two mirrored (I mirrored them in the slicer).

Printed with PLA on a Prusa CoreOne with 10% 3D Honeycomb infill and .4mm layer height.

Created in OnShape: https://cad.onshape.com/documents/cce0a30d12f7053916fdf8e2/v/abf59fc637e2d9f2542b1ef9/e/b823ab44f2b5de1fc1b64dda

The files are are V1 in Onshape, and are use for the rear brackets in the photo. V2, visible in the front brackets in the photo, has a cutout to accommodate the flanges that support the shelf on my desk; I did not upload these files as they are specific to my desk.