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This joint is commonly and widely used. Ductile Iron pipes comprise of socket and spigot ends. The inside surface of the socket has grooves to hold the rubber gasket. The gasket has a hard part called the 'heel' which gets engaged in the groove of the socket to firmly hold the gasket. The other part of the gasket is the bulb portion which is comparatively softer than the heel portion of the gasket. Both softer bulb and the harder heel portions of the gaskets are vulcanized to form a circular single part. The spigot of the next pipe has a taper portion to facilitate smooth insertion of the spigot end in to the socket of the pipes. The spigot is inserted into the socket holding the rubber gasket. The spigot exerts uniform circumferential pressure over the soft portion of the rubber gasket and the pipe is pushed in to the socket until one line of the insertion mark gets into the socket and the other insertion mark is visible. This is to ensure that a small gap is left between the two pipes in order to ensure the deflection in the pipeline and also to accommodate the linear expansion due to thermal effect on the pipeline laid above ground. In this fashion the pipeline is made continuously.