A metal lined composite overwrapped pressure vessel comprising: (a) a liner constructed from a metallic material and comprising: (i) a liner orifice; (ii) a liner neck region surrounding said orifice and having an outer surface, the outer surface of the liner neck region comprising a male threaded element; and (iii) a liner polar region surrounding said liner neck region; and (b) a polar boss constructed of a second material and attached to said liner neck region of said metallic liner, wherein said polar boss comprises: (i) a polar boss neck region having an inner surface, the inner surface of the polar boss neck region comprising a complementary female threaded element, wherein at least a portion of the inner surface of said polar boss neck region is attached to at least a portion of the outer surface of said liner neck region by having said complementary female threaded element engaged onto said male threaded element; (ii) a passage within said polar boss neck region that is coaxially aligned with said liner orifice; and (iii) a polar boss annular flange that covers at least a portion of said liner polar region, wherein said second material has static strength, fatigue strength, endurance, chemical resistance and/or corrosion resistance greater than that of said metallic material, the top portion of said complementary female threaded element of the inner surface of said polar boss neck region being configured for threaded connection to a port fitting device; and (c) composite overwrap material encapsulating the liner and at least a portion of the polar boss. (a) a liner constructed from a metallic material and comprising: (i) a liner orifice; (ii) a liner neck region surrounding said orifice and having an outer surface, the outer surface of the liner neck region comprising a male threaded element; and (iii) a liner polar region surrounding said liner neck region; and (i) a liner orifice; (ii) a liner neck region surrounding said orifice and having an outer surface, the outer surface of the liner neck region comprising a male threaded element; and (iii) a liner polar region surrounding said liner neck region; and (b) a polar boss constructed of a second material and attached to said liner neck region of said metallic liner, wherein said polar boss comprises: (i) a polar boss neck region having an inner surface, the inner surface of the polar boss neck region comprising a complementary female threaded element, wherein at least a portion of the inner surface of said polar boss neck region is attached to at least a portion of the outer surface of said liner neck region by having said complementary female threaded element engaged onto said male threaded element; (ii) a passage within said polar boss neck region that is coaxially aligned with said liner orifice; and (iii) a polar boss annular flange that covers at least a portion of said liner polar region, wherein said second material has static strength, fatigue strength, endurance, chemical resistance and/or corrosion resistance greater than that of said metallic material, the top portion of said complementary female threaded element of the inner surface of said polar boss neck region being configured for threaded connection to a port fitting device; and (i) a polar boss neck region having an inner surface, the inner surface of the polar boss neck region comprising a complementary female threaded element, wherein at least a portion of the inner surface of said polar boss neck region is attached to at least a portion of the outer surface of said liner neck region by having said complementary female threaded element engaged onto said male threaded element; (ii) a passage within said polar boss neck region that is coaxially aligned with said liner orifice; and (iii) a polar boss annular flange that covers at least a portion of said liner polar region, wherein said second material has static strength, fatigue strength, endurance, chemical resistance and/or corrosion resistance greater than that of said metallic material, (c) composite overwrap material encapsulating the liner and at least a portion of the polar boss.