Use the ERGO Adaptor to install an AR stock/brace & pistol grips on your Mossberg 500/590 shotguns. Accommodates mil spec or commercial buffer tubes. ALL NFA RULES APPLY Compatible with both 590 Models & Shockwave. Use any style AR stock/brace and pistol grip combination ALL NFA RULES APPLY Accommodates mil spec or commercial buffer tubes This adapter has the proper drop designed in, so factory sights can be used. (Bead, Rifle, and Ghost Ring Sights) Made from glass filled polymer Includes mounting hardware Torque specifications for grip screw is 25-30 inch-pounds. DO NOT EXCEED. Product damage can occur because of over tightening. Mfg: Ergo Grips