Buttweld Fittings general. A pipe fitting is defined as a part used in a piping system, for changing direction, branching or for change of pipe diameter, and which is mechanically joined to the system. There are many different types of fittings and they are the same in all sizes and schedules as the pipe.

A Socket Weld is a pipe attachment detail in which a pipe is inserted into a recessed area of a Valve, fitting or flange. In contrast to buttweld fittings, Socket Weld fittings are mainly used for small pipe diameters (Small Bore Piping); generally for piping whose nominal diameter is NPS 2 or smaller.

Socket Weld (SW) fittings are defined in the ASME B16.11. As with socket weld, a pipe is inserted into a recessed area of the fitting. … They are welded at their ends to pipe end, with the same thickness as pipes. The end of butt weld fittings shall be beveled.