Forged iron piping was typically produced with one spigot stop(plain) and 1 socket or hub end(cup shaped). In use, the spigot of one phase was positioned to the socket in the preceding one particular and a hoop of oakum was pressured down to the joint by using a caulking iron. http://cesarwgkep.bloginwi.com/15865191/5-essential-elements-for-valves-and-fittings