I used these for a wooden rack I built, because I thought the flexibility to mount 19" devices at varying distances would be important. In practice most devices adhere to the standard height units and if not, you just have to remove rubber feets or similar. Fitting the nuts and aligning them with holes of the rack ears can be _very_ fiddly. Be sure to use a rubber strip inlay. Or just use a rack strip with standard distance holes instead.