The instructions said to cut a longer and slightly wider slot on the cutout end by 3/4" and then grind off the internal ribs so the forearm could slide over the tube correctly. I took the gun apart and tried the install, I just didn't feel comfortable hacking the ribbed forearm up. It should be made correctly from the factory to begin with. I also bought a pistol grip a few weeks ago that was suppose to fit a remington 870 12/20 gauge, the supplied adapter had to be modified with a dremel per the instructions to fit properly. When I buy a product designed for a specific gun it should fit as advertised, not need to be modified with cutting and grinding in an area that is visable to the eye after the install. Just my 2 cents, but I will never buy another ATI part again!