A bracket designed to have 1/2" PVC pipe (sch. 40 or sch. 80 both are .840" OD) snapped into it to form a shelf for filament spools or most anything else. Spools can be slid back and forth without hitting the bracket. Spools turn easily on the PVC so printers can be fed directly from the shelf.  Mount bracket in front of wall studs, if possible, for added strength.  Two flathead screws are required for mounting.