Two-piece drop-in rail system hand guard for AR-15 carbines. The hand guards are removed and the 2 piece quad rail is attached. Excellent reviews for this piece of equipment. If you are looking for a quad rail for your weapon, I would suggest looking at this. Amazon has this at a good price, especially these days, and you can see it here, and read the reviews.
Global Military Gear AR-15/M4 Aluminum Quad Rail
Product Dimensions: 2 x 6.3 x 9.3 inches