I am looking at a job where the fixtures are supported by a nipple thru a 4" sq. blank cover (52C6) which in turn is mouted to a 4" sq bx.
Does this meet the requirements of 314.27 ??
I believe it is a judgement call, I personally have done it and seen it done a lot in my area. Obviously the fixture should not be very substantial. You could argue that a 4sq blank with a factory KO is intended for this use.