“Standards are great. That’s why we have so many.” Clever sayings are great. That’s why they’re so overused. It is always unsettling, however, when you discover something you thought was a standard isn’t always accepted everywhere. Today’s question:
“With regard to rack rails, apparently there is a standard for Europe and another for the USA. My question is what is the difference? And, for someone who works with one foot in both, what problems/solutions are there?”
The standard we use for rack equipment is established as a 19 inch width between the center of holes on opposite rails, with 1.75 inches designated as the “standard” height of a space, and a screw thread configuration known as 10/32. 10/32 relates to the size of the screw and the density of the threads on the screw. The first number is the diameter and the second number is threads per inch (or millimeters if it’s a metric sized screw). If you’ve ever stuck a machine screw into a threaded hole, had it fit, but were unable to turn it more than a half turn you have encountered a difference in thread density. The 1.75 inch spacing is commonly known as a “rack space” or “rack unit.” As most know, our rackable equipment height is often stated in rack units, such as 1U, 2U, 3U, etc.
That’s our standard. What we mean by “our” standard, however, isn’t so much a national standard as it is an industry standard. There are (surprise) other standards that have been used in other industries. The telecommunications industry, for example, has been known to work with equipment that is 24 inches wide, and/or with a 10/24 screw thread configuration. In some older audio racks you will encounter the 10/24 thread configuration as well. The military has their own book on standards and they can sometimes deploy equipment of other odd sizes. Some parts of the hi-fi industry have tried things, but none of them ever stuck.
In the domain of the typical “pro audio” we are likely to encounter it is generally safe to assume rack rails and equipment are going to correspond to the dimensions outlined above. The most likely difference you will encounter is some variation to the screw thread so you may want to keep some alternates around. A drill can be handy for making some last minute modifications to a rack as well. Otherwise there’s not much you can do and not much reason to worry about it. If you run into a rack where your gear will not fit, or into some gear that will not fit your rack, the solutions are pretty limited and obvious.