This is mountable (4 through holes in the rear face) junction box designed to securely hold a standard 8-gang relay module with 4 screws (picture was taken before the module was secured but the screw holes line up perfectly), complete with lid (uses 4 screws to fasten). There's 1" (25mm) of clearance inside the box above (signal input) and below (relay connections) the board for enough space for wiring to be routed, and the lid, while 5mm thick for strength, sits only 3mm off the top of the box (recessed the other 2mm) and very close to the top of the relays, for the lowest profile possible.  One face has two 10mm holes, large enough to hold lamp cord wires (18AWG 2 doubles and 1 single each). The opposite face has one 10mm hole and works well for shielded CAT5 cable for signal input, along with a few other small gauge wires (module power, test wire, etc.) that you may need to squeeze in as well.

Print box with rear face down, no supports, and lid with front (outer) face down.

Overall (box and lid assembled) dimensions: 149.5mm X 106mm X 29.5mm

I included another box with two additional 10mm holes, in case your intended purpose needs it.

The box wasn't designed with strain reliefs in mind, but if you need to secure the wires so they can't pull out of the box, an inelegant but cheap and effective solution is to simply wrap a zip tie around the wire where it exits the box, and tighten as much as you can. I feel like this is more compact and space-saving than electrician's knots - especially because you can use one zip tie at each port, holding all the wires using that port instead of tying each wire into a knot.

I know this isn't a very complicated design but please share your makes! I love seeing other people's printed models of my designs!

You may notice some defects in the one I have pictured. These are printing defects, not design issues. If I needed my print to be perfect, I would consider the one in the picture to be a failure. Since functions as intended, isn't intended to be seen, is being used inside a vending machine, and even the few people that do see it aren't likely to notice (or even care), I decided to use it rather than postpone my wiring project another 5 hours (with my un-tweaked Neo 2 settings) to print one with the only added benefit being it's “prettier.”