Stub finishes are used with lap joint flange. In such a flange, the stub is butt welded for the pipe, While flange is freely moved over the stub close. It is largely flange aspect but lined less than ASME B16.9 which is why it is regarded as pipe fittings. This http://messiahwhnty.isblog.net/5-essential-elements-for-pipe-fitting-11808652