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. For even less friction, search "spool roller by heavynets". Overall dimensions are about 7.5" (191mm) x 6.5" (165mm) x .5" (13mm). It's the cheapest way that I have found to make a shelf. Two flathead wood screws are required per bracket.