Built for simplicity, not sturdiness, so don't expect it to hold a lot of weight. The parameters in the included F360 file should make it easy to tweak any dimension you need to get a perfect fit, but I included a batch of possible sizes which you might want. Cover photo is the D80 with Octogram Spiral top and bottom fill patterns.

Notable features:

• Separate wall mount piece makes it easy to install and then slide the main shelf into place on top.
• Wall mount includes countersunk screw holes.
• Supports only needed for underside of main shelf piece where wall mount slides into place, not visible after installation.

Parameter notes:

• Main parameters that you're likely to tweak are mentioned in red in the one image.
• The ‘wiggle’ parameter determines how much of a gap there is between the wall mount piece and the shelf piece that slides on. Current value feels like a perfect fit on my MK4S, but if it doesn't slide right on for you, increase it.
• Screw dimensions can be entered to get perfect countersinking flushness,  but the default is pretty generous.
• The gap between the screw holes (hook_screw_gap) auto-increments of steps of 20, meaning you'll be able to use the same screw holes in your wall if you print a few similar-but-not-quite-the-same sized shelves in a row, without having to re-drill wall holes.

Use “Supports on build plate only”.