Mounting Hole: 20.2 mm ?????

[platypus2020]

The panel builders at work, just use the 13/16" step on one of the larger step bits, for the 20 mm switches and lights

[Willy]

Let's not confuse this issue with common sense approaches when a perfectly sized 20.2mm taper shank drill is available.
It's almost like it was preordained. There's a reason they make these at precisely 20.2mm, and Paul has the answer.
By the looking at these bits they should be good for at least a few holes in panel material.

[Paul Alciatore]

Not really, if you do a search for this type of switch, you will see that there are many that have that exact same mounting hole spec. Different switches and different brands. It seems to be some kind of standard for a "push in" mount switch.

Last night I found a suitable taper reamer on E-Bay and ordered it. I will drill 20 mm with a metric step drill and ream it if necessary. I can't wait to see if it fits in a 20 mm hole or if I really have to widen it that extra 0.2 mm.

It's possible it was supposed to read 20.0 mm and the persons finger just slipped. The zero is a double width button on a numeric keypad
overlapping both the 1 and 2 buttons.

[CCWKen]

They were probably designed/made using a Chinese ruler. They're cheap because they're out of common spec. Perhaps to match the Chinese punches and drill bits.