Alright. I tried searching cause apparently I'm not smart enough to figure it out. What tool do I need to loosen it so it will fit over the flattop rails on my RRA M4. I can see that if you losen one side, it expands out. I tried a flathead screwdriver but that didn't seem to do anything. It seems pretty stiff when I tried to turn it and the screw drive popped out of the groove.

You're on the right track...

I used a flathead screwdriver and took the slotted nut all the way off.  The I slid the sight into place, put the the square bolt through the slot and tightened it down.  Oh, I also used a drop of the red Loctite that came with my SIR 50.

[img]http://a8.cpimg.com/image/5A/C9/19917658-eab7-02000180-.jpg[/img]

[img]http://a2.cpimg.com/image/5E/C9/19917662-e752-02000180-.jpg[/img]

Alright thanks for the help. Finally got it. Took the charging handle out and it finally just slid right on :)