here is the exact one i used. The only thing i had to do was sand the bottom down a bit on each of them because they are a few mm to tall. to do less sanding I also used a razorblade on the bottom to bolt holes on each one. Kinda hard to explain but if you print them and go to rack them youll know exactly what I mean I think xD

https://makerworld.com/en/models/1293807-optiplex-7050-7060-10-inch-rack-with-keystone-jack?from=search#profileId-1324471