Description The Centurion patented C4 rail system is a lightweight, rugged, 2 piece free float rail that when installed gives the uppers a continuous 12o'clock rail. The C4 system is the lightest and most rigid rail that clamps to a standard barrel nut on all AR15, M4, and M16 type weapons systems. This design allows the installation of the rail on an upper assembly without removing the front sight post or permanently attached muzzle devices. Specifications:7 inchWeight: 8.7oz with screws---1.1oz with standard barrel nut Length: 7.3in Width: 2.1in Height: 2.38 Inside diameter: 1.37 9 inchWeight: 10.6oz with screws---1.1oz with standard barrel nut Length: 9.25" in Width: 2.1in Height: 2.38 Inside diameter: 1.37 10 inchWeight: 10.7oz with screws---1.1oz with standard barrel nut Length: 10in Width: 2.1in Height: 2.38 Inside diameter: 1.37 12 inch Weight: 14.2oz with screws---1.1oz with standard barrel nut Length: 12.565in Width: 2.1in Height: 2.38 Inside diameter: 1.37 ***Please Note***- Screws are included with the purchase of all rail systems. Replacement screws are available to purchase if necessary. *** We recommend gunsmith installation for all of our parts. We cannot warranty items damaged by improper installation. Custom Cerakote Disclaimer: Custom Cerakote is completed per order. Our Cerakote room runs one color at a time so your ship date will be subject to the color rotaion at the time the order is placed. You will receive an email confirmation once the item has actually been packaged to ship. Cerakote items are not guaranteed to match separate batches or Cerakote completed by outside parties. While we strive to keep our mix uniformed for our own products, we can't say for certain what Walter and Jesse cooked up in their lab out in Albuquerque.