The socket weld flange is similar to a slip-on flange, except that it has a bore and a counter bore. These act as a socket, holding the pipe in place before welding, hence the name. The counter bore is slightly larger than the OD of the matching pipe, allowing the pipe to be inserted into the flange, while the diameter of the smaller bore is the same as the ID of the matching pipe. This difference in the bore size acts only as a restriction to the depth insertion of the pipe, and therefore eliminates any restriction in flow.