A SMART equipment manufacturer will make his faceplate slightly smaller than 19″ – such as 18-31/32″ to avoid any problems with rubbing in tight racks.

I once had an AP Audio patch bay that actually measured 19-1/32″ and would not go into my all-steel welded rack (Premier or Bud). I e-mailed the mfg. and they said they saw no problem with it becuase no one else had complained before! Well, not everyone has cheap plywood racks with enough ‘give’ in the sides.

By the same token, I suppose a smart rack manufacturer would error a little on the wide side when spacing his (recessed) rails.

This kind of goes along with Jakob’s statement above where he notes “What is truly missing from this article are actual tolerance ranges for each number”. Amen!

That said, this article commits the deadly sin of randomly rounding specifications differently and inconsistently. If you want to be inexact, do it consistently. 18.312″ (465.14mm) OR 18.31″ (465.1mm) OR 18.3″ (ca. 465mm) OR 18 5/16″ (ca. 46 1/2 cm). The ca. (circa) in front of 465 mm is needed because 465 looks like a human-chosen exact specification, even though it is not.

What is truly missing from this article are actual tolerance ranges for each number (e.g. the center distance of holes should be at least 18.???” (46?.? mm) and at most 18.???” (46?.? mm) but in reality varies between 18.?” (46? mm) and 18.?” (46? mm).