As the video explains, the most common pipe branch connections include stub-in and stub-on connections. With a stub-in connection, drill the larger hole in the header pipe. The contoured end of the branch pipe fits inside the hole. You then weld the two together at the connection.
A stub-on connection uses holes of the same size. Since the header or run pipe hole and the branch pipe hole have the same size, the branch pipe sits on the header pipe.
It is important to know when you use each of these piping connection types. When your header pipe and your branch pipe are equal in size, meaning that they have the same diameter, you use the stub-on connection. When your branch pipe has a smaller diameter than the header pipe, you use a stub-in connection. Using the wrong type of connection can cause problems. While stub-in provides the stronger of the two connections, you should only use either option in a situation with low-pressure and low-temperature fluids. Neither replaces the piping and joints with three times welding required in high-pressure fluid situations.