The straight tee is a three-way fitting used to make perpendicular connections to a pipe. Its name comes from its resemblance to the letter T. The straight cross is a four-way fitting used to make double perpendicular connections to the pipe. It resembles a crossroad. Lines that connect to the main run of pipe are known as “branches”. The main run of pipe is often called the “header”. The word “straight” denotes that all three (for tee) or four (for cross) outlets are the same pipe size.