A note on dimensions. The magic of "standardization" has firmly ensured that a 19" rack actually has no 19" wide components. Also, a 2x4 isn't really 2x4.
I have attached an image which I shamelessly took from
As for the venerable 2x4, it now measures 1.5" by 3.5". Go figure. Some folks say it's because the lumber is 2x4 before planing and drying. I say, it's Fun Size!
PS: This started out as a TOTALLY SRS BIZNSS PROJECT FOR HACKADAY PROJECTS I SWEAR. But somewhere between the beginning and end of filling this out, I realized I was describing "get some boards and screw them together" as though it was the greatest thing ever. At least I have more things to bug the dev team about, right?