I was initially inspired by this model. However, the M6 nuts I got were not quite the right size and I had some other nit picks with the component tolerances, so I decided to make something that fit my needs from scratch!

I designed the model to fit a US standard 10x1 plank of wood. The tolerances are such that an untreated, off the shelf plank should fit, but it might be tight. I sanded the plank I got fairly thoroughly so I could stain and clear coat it, and it actually turned out a little loose. I included clearance holes for wood screws, so this wasn't an issue for me since I just secured the slightly loose plank with the screws after I got the spacing between the legs ironed out. I used #8-3/4" flat head wood screws I found at Lowes while buying the plank of wood. If you use these same size screws, I found that an M2.5 drill bit provides a nice pilot hole so you don't split the plank. 

The rack mount portion is designed for M6 hardware. I used M6x20 BHCS and they should have plenty of real-estate to engage with the nut for most rack mounts. The square nuts I got are about 5mm thick, and they had a nice friction fit into their slots and wouldn't fall out on their own. This can likely change due to print settings or the specific nut vendor, so I've included a test block you can print to ensure your nuts fit before committing the time and material to print a whole thing. 

I included the .step file for the riser too in case any modifications are needed. There is one with no hard edges (it is just the .step version of the .stl file), and there is a version with the hard edges included. I find the hard edge versions of .step files easier to modify. 

This is designed to fit on a Prusa Mk3.9/Mk4. I printed in PETG, though PLA would also likely work just fine.