My desk is slightly slanted, and the sliding under-desk CPU mount (one like this: https://www.amazon.com/Safco-Products-2175-Ergo-Comfort-Swivel/dp/B000YA1LJ0/ref=sr_1_35?dchild=1&keywords=mount-it+cpu+holder&qid=1611781017&sr=8-35 ) likes to slide forward. Then i bang my knee when I'm getting up from my desk.

So I printed this holder to keep the CPU from rolling forward on the bearings. As with anything, your mileage may very.

forgive the heat warping on my print -- i'm messing with some dodgy PLA that seems to hate printing at normal temps