Bravo Company 13 ALPHA Keymod Rail, Fits AR Rifles, Aluminum Alloy, Includes BCM KeyMod Sling Mount and a BCM KeyMod Nylon Rail, Black BCM-KMR-A13-556-BLK Bravo Company's BCM KMR ALPHA 13" KeyMod Free Float Handguard is manufactured from aluminum that is lightweight yet durable. It also features a proprietary patent pending mounting indexing and lock up system that mitigates 12:00 rail movement under heat generated from the barrel nut. Inner diameter is 1.3 inches and the outside is 1.5 inches flat to flat. The handguard flares forward (towards muzzle end) at the 3 and 9 O'clock positions approximately 1/4 inch and the actual length when measured to flare is 10.5 inches. The KeyMod interface system was developed by Eric Kincel (now the Director of BCMs' product development team) to work in parallel with the current picatinny system. In many applications it will advance modularity past the current 1913 rail system. The BCM KMR Alpha also allows for a larger range of modularity offering 4 different offset mounting positions between traditional 3" 6" 9 and 12:00 positions. In the most basic of applications the KeyMod system allows for universal modularity between various manufacturers of accessories and accessory rails. A big win for the trigger puller.