Constructed by BrassMust Needed for Your Precisse Adjustment Between Magazine Gas Lip and PistonCompatible with Tokyo Marui OEM M4 Magazine, DyTac AR Style MWS Magazine, Xmag, Shadow2 and DyTac 9mm SMG GBB MagazineThickness : 5 x 0.1mm / 5 x 0.2mm / 5 x 0.3mm