The rails that attach to the stock hand guard do so with a "nut" that has a flange on it. The "flange" keeps it from falling through the hole in the hand guard. I have one on my DMPS. While it does work, it was a pain to install because the glacier guards are thicker than M4 or carbine style guards. Tightening them down isn't the easiest thing to do because you have nothing on the "flange" to grab hold of. I had to use a longer allen screw, pair of pliers and a lock nut to get it to work. Not the greatest set up, but it does it's job of attachment point for the bi pod.
"The history of our race, and each individual's experience, are sown thick with evidence that a truth is not hard to kill and that a lie told well is immortal." Mark Twain
"Passive acceptance of the teacher's wisdom is easy to most boys and girls. It involves no effort of independent thought, and seems rational because the teacher knows more than his pupils... Yet the habit of passive acceptance is a disastrous one in later life." Bertrand Russell