DescriptionThe 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. **Please note that some FSBs may need to be modified to fit by filing down the longer sling attachment ears so that they are not touching the handguard **Please Note: Current version of the rail has some slight cosmetic differences from stock photosEngraving is now machine engraved and black anodized....no white markings. Features Material: 6061 T6 Finish: type 3 hard coat anodized Weight: 10.5oz with screws---1.1oz more with standard barrel nut Length: Top 7.25 in Sides 9.5 in Bottom 8 in Height: 2.38 Inside diameter: 1.37 Rails: 1913 spec rail Fasteners: grade 8 bolts with phosphate finish MADE IN USA ***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.