This is AWESOME! They're as thick as drywall, so cut a hole and stick it in. It doesn't matter if 2x4s get in the way of cutting the hole - they still fit! Basically, if you can run a wire across the ceiling, this is your best bet for adding can lighting to your space. Knockout through which you stretch the Romex. This is EXCLUDED. I prefer the plastic ones, so if you need one, search "Push-in NM Cable Connector 1/2 inch". (I still give the product 5 stars) I ran into a problem: I cut a hole in the ceiling and there were TWO 2x6s in the way. In THAT case I struggled to get the light on, but a 2x6 on the trail is fine. I also ordered 48 more of these. They go EVERYWHERE! If you are installing multiple of these, I also highly recommend searching for "Dustproof Adjustable Hole Cutter". Have fun installing!