Our M10mm Stainless Steel A4 Hex Nut is a replacement upgarde for ZR part number FB02013. This is a true Marine Grade 319 (A4) Stainless Steel Hex Nut that is specifically intended for use in a Marine enviornment. An intended compliment for our M10 x 50mm A4-80 Bolt for the v2 & v3 ZR U Pipe and Second Generation Quick Nozzle.