Luth-AR 308 Barrel Nut Black 308-BL-16. 308Barrel Nut is made for DPMS pattern upper receivers and is 1-7/16 x 16TPI (DPMS). Specifications for Luth-AR Barrel Nut .308: Manufacturer: Luth-AR Color: Black Gun Model: AR-10 Finish: Anodized Caliber: .308...