Today at work I had further confirmation that "standard" is not necessarily standard. We purchased a few rack mount servers recently, and also a rack to place them in. Today it was time to assemble the rack and test the rack mount kits in it to ensure everything would fit before deployment date.
Arrrgh. Even though it's a standards-compliant rack, Dell's rack rails wouldn't fit into the rack as it was. The rack has two parallel rows of square holes at each leg, instead of having only one as Dell assumes. This means that Dell's "clever" rack-mount kit, which can be adapted to either square-hole or round-hole rails, can't be inserted.
I had to take a big-ass pair of pliers, and bend the inner row of square-holes out of the way to install the rails.
This is why I like to test fit and finish for everything before the downtime window. Dealing with this crap when you're pressed for time is NOT fun!