My personal feeling is that equipment should not come with concentric knockouts.
The company I work for orders all panel tubs, troughs and cans with no knock outs.
If your an electrician you should have the tools to make the holes the right size and where you need them.
This picture is a perfect example of why, if I was forced to use for this rubber cord I would install reducing washers over the entire concentric KO.
Now why is there rubber cord hanging from this disconnect anyway. 400.8(1)
