The wide construction of the NEMO 556 handguard provides superior heat shielding, as well as the ability to accommodate custom builds with suppressors. Caliber: 5.56 NATO Height: 1.216 in (bore centerline to top of rail) Length: 15" Exterior Width: 2.22 in Inner Diameter: 1.83 in Large inner diameter accommodates many under guard suppressors (1.83 in) M-LOK(TM) slots at 3,6, and 9 o'clock positions accept M-LOK compatible accessories. Integrated rail at 12 o'clock with engraved T-marks 6061-t6 aluminum alloy extrusion Mil-Spec hard anodize type 3 (black) Integrated rotation limited steel quick disconn Mfg: Nemo