Square holes vs round

A typical section of 19-inch (482.6 mm) server rack rail
A typical section of 19-inch (482.6 mm) server rack rail (image source; wikipedia)

Square hole racks are going to give you less trouble when mounting equipment. For starters, every major equipment manufacturer is going to have rails that work either exclusively with square hole, or have some quasi-compatible setup for square/round where the rails don’t fully seat against the ears of the cabinet. They do make conversion kits out there for round hole to square, if you’re into that sort of thing. Personally I stay away from conversions, as they’re just another thing that can break, or not be delivered on time, or weren’t included with the PO, etc.

Next, while cage nuts can be a bitch, there are [simple] tools that make using them a breeze. I keep a few of those 10-cent shims in my bag, and can fit a whole rack with cage nuts in about 10min – or clean one out in about a minute. They get a bad name because people try using the wrong tool for the job (IE: screwdrivers, pliers, knives, etc). In IT, the right tool for the right job – period.

Third, there’s the topic of re-use. If you’re never going to be moving equipment around, then the type of hole only matters from a compatibility standpoint. If there’s going to be occasional re-work done, then square hole should be preferred because it will last significantly longer. Compared to threaded round hole where you have to break out a tap and dye set every now and then to fix the threads. It’s much easier in the grand scheme of things to just remove a cage nut and install another.

With the exception of large telco racks, I don’t think I’ve seen an actual 42U round role rack in years. Square hole racks dominate the market. I’m sure they can still be found on Craigslist next to the old refrigerators, rusted trucks, and PE2950s – but even then they’re less and less common compared to squares.

Author; ghostalker47423Datacenter Engineer