Ok I admit my ineptitude. I have a Sig 556 Holo, it has the collapsing folding stock and the plastic tube. I really dislike the rattling stock from Sig. Not that it hasn't worked it just annoys me. I got a new Magpul CTR in trade, was able to compare the Mil Spec to the Civilian and the civilian seems to be the right size but have no idea how to attach this. Somebody help? Do I need a buffer tube? If so how do I take off the tube from Sig?