I downloaded the shelf brackets because they were just right for my needs, but I didn't realize they were honeycomb (DOH!), I needed them for my Multiboard setup, so I remixed just the insert in TinkerCad and you have the result you see. There was not enough space to put 3 Snaps there, so I centered just 2.

For my setup (to hold up reels of filament), I thought it prudent to add screw holes and countersink them.

The screws are the M4.5, but there is enough meat around the screw hole to make the countersink or hole bigger.

Happy Printing.