First off, reducing washers are heavily used in my side of the biz. (Cinemas) Mainly on the flex for the DC leads to the Xenon lamp, though. Seems that the manufacturers of that equipment can't get on the same page and design a standard KO size for a given lamp type.

And did any of you catch the doublespeak in this from the UL white book? (Bold emphasis is added by me.)

Quote
GROUNDING
Metal reducing washers are considered suitable for grounding for use in
circuits over and under 250 V and where installed in accordance with
ANSI/NFPA 70, ‘‘National Electrical Code.’’

Stupid should be painful.