The Unions are designed to quickly join mud tanks without the work associated with flanged connections. Even if the tanks are not aligned perfectly,  Hammerseal Unions can still be made up tight for a non-leak seal. The externally threaded female portion of the union welds to a stub of pipe at the tank wall. Connecting pipe extends through the nut, the macro o-ring and then into the female. When the internally threaded nut is hammered tight onto the female, the captive o-ring is compressed into a "D" square cross section, sealing fluid pressures up to 150 psi against the outside diameter of the connecting pipe.