LBE Unlimited Handguard Cap, Round, Fits .750 Barrels, Black ARHCR The LBE Round Handguard End Cap fits .750" Diameter Barrels. The handguard end cap installs behind your FSB (front sight base). Original style handguards and many aftermarket style handguards require a round or triangular end cap. LBE Unlimited is a leading producer of US Made gun parts and accessories.