This is a UTG Pro drop in rail for a CARBINE length gas system that uses the ROUND end cap. This is a sturdy little rail that is slimmer than most polymer rails out there. It is NOT the mlok version. It uses a proprietary system to attach picatinny sections along the rail where you want and only picatinny accessories will work with this rail. Comes with 2, 4 section pieces and 2, 2 section pieces. This is an affordable, made in the USA, rail. I will include a chopped Magpul vertical grip as well. $50 firm, willing to ship for an extra $10.