4 inch tank openings reduced to 2 1/2" x # 8 NPT female Thread and o-ring ( for 4" side of adapter to tank ).The 4" MPT fitting screws into tanks with 4" female opening, and allows the use of a smaller valve ( one with 2 1/2" male threads ) to be used.Allows use of standard valves to be used on commercial size tanks.Note: Newest version ( round = Wave Cyber glass filled Noryl ) appears to be about 1/4" taller than the old version ( flat octagon ).Structural Compatible.
