I fail to understand why manufacturers can't get concentric KOs right. Twice yesterday, the entire KO ring blew out while I was trying to remove just the center. Now I have sets of 2" --> 1" and 2" --> 1-1/2" reducing washers installed. I hate these things with a passion. Just let me punch my own holes if it's so hard to engineer a concentric KO that isn't terrible; at least then I know they'll always come out the right size. That's why I always buy enclosures with no KO's.
The concentric KO's in 4" sq. boxes work great. Why can't that technology be applied to breaker panels and ATS enclosures?!