The Latest PRI Gen III AR15/M16 Freefloat Forearm and barrel nut are constructed of light weight high strength carbon fiber, aluminum and high strength steel for the best possible combination of weight and strength. The carbon fiber also reduces the amount of heat transferred to the shooter's hand during rapid or high volume firing. The long top rail matches the height of the top rail on the standard flattop receiver and is compatiable with the ARMS family of rails. The most rigid M16 freefloat system available is now easier to install. The forearm weighs 1 lbs. with an internal diameter of 1 3/4" at the open end of the tube. The overall length of the forearm is 12 1/2". SPR* is a registered trademark of ArmaLite Inc. and is used under license agreement.