These flanges have a bore and counter bore dimension. The counter bore is slightly larger than the O.D of the matching pipes, allowing pipes, allowing the pipe to be inserted into the flanges. The diameter of the smaller bore is the same as the I.D of the matching pipe. During assembly, the pipe is inserted in the larger diameter bore andis welded in place. This type of flange is often used with high-pressure systems that use smaller diameter pipes. These flanges application is in Chemicals, Hydraulics and Steams plants.