Changing my review a little. - Pro Mag AR-15 / M16 9MM Magazine Adapter Block For Colt 9mm SMG Magazines, Quick Change

The one I received came with no instructions. Maybe a return? Anyway, I looked up the Youtube video on how they say to install it. I now see why they call this a "two piece" design, because they recommend punning the front feed ramp portion off, jamming the back piece in, pushing it rearward, and then sliding the feed ramp portion back on. I tried doing this on my Essential Arms receiver and it's really tight. Like it feels like it'll break tight when you go jamming the rear half in the magwell. It just doesn't fit because of the hump on the side and the tabs on the top. I'm sure I could probably get it in that way, but it would distort the heck out of the rear portion doing it. I recommend using this thing as a top loader and do the replacing the roll pin with an "R" clip thing if you're going to be switching it back and forth. It's WAY faster. So I guess you could say this thing is "sort of" a two piece, but not the kind of two piece that gets pinned in place or held in with screws. I seriously wonder if everyone who had one break caused it by jamming it in from the bottom? Be aware AR magwells are (used to be?) all over the place as far as fit goes. It might work fine in a loose one. I have an Olympic receiver that the adapter won't even fit in from the top, but it's not surprising since a lot of mags fit super tight in it, and sometimes need to be sanded on to get them to fit.