I don't like that rail system too much, it made my saiga inoperable for a while and I couldn't figure it out.
It mounts by squeezing the the gas tube.
Get the chaos rail if you can, they're on sale now so they're cheaper AND better.
http://www.chaosus.com/cgi/commerce.cgi?preadd=action&key=EXTENDED_QUAD_RAIL
That one is really sweet and man is that one hell of a deal! I just dont have the cash for it right now.
Any idea how long it will be that price for?
It was a July sale but the deals are still up, so get em while you can.