Is there a "correct" way to install knockout reducing washers? When I install the outer washer I put the lip down into the knockout hole, and the inner washer with the lip also down (facing the inside of the box) so the lip of the outer washer sits in it. I was told the lip of the inner washer should face up so it butts against the outer washer to fill in the gap. Then I was told either way is acceptable. In both cases the fittings tighten with no problem.

The intention of the dropped ring near the center, or lip I believe your referring to, is to take up the space of the thickness of the metal box.

So, both washers should be placed opposite of each other so the dropped ring fills in the space.

TK,

The more I thought about it the more it makes sense to install the washers opposite each other as you described. Thanks for confirming... shader