Slim, lightweight and nice feel in your hands - Radical Firearms M-LOK Slim Rail System (FCR)

This is a nice slim, and lightweight rail. Fits well in your hands, especially for 'thumb-over' grip near the muzzle of your rifle. However, Tightening the barrel nut was somewhat of an issue. Using a standard AR Wrench is not the advised way to install/tighten; even if the instructions tell you to use it. The metal is soft and you risk mushroom'ing the screw holes; which I did. I had to file the metal to get the rail to fit properly. Use a large open-end wrench.