ANSI B16.5 Class300 Loose Flanges are used with a corresponding stub-end that "inserts" in the inside of the flange. The main benefit of this type of flange, is that once the pipe welds to the insert stub-end, the flange then can rotate for easier alignment of the bolting holes.However, lap joint flanges and their stub-ends' ability to hold pressure is about the same as slip-on flanges.
