The socket welding flange is similar to a slip- on flange except it has a bore and s counter bore dimension. The counter bore is slightly larger than the O.D. of the matching pipe , allowing the pipe to be inserted into the flange similar to a slip-on flange. The diameter of the smaller bore is the same as the I.D. of the matching pipe A restriction is built into the bottom of the bore which sets as a shoulder for the pipe to rest on. This eliminates any restriction in flow when using a socket welding flange.