Tees are generally measured from the "Run" to the "Bull". The "Run" is the left-to-right or the length of the Tee. The "Bull" is the top part of the Tee. For example if a Tee is 3/4" X 3/4" X 1/2", then the left inside diameter is 3/4", the right inside diameter is 3/4" and the top inside diameter part is 1/2".
branch tee (plural branch tees) A tee pipe fitting with female connections on the two straight ends and a male connection on the branch.
Pipe Tee is a type of pipe fitting which is T-shaped having two outlets, at 90° to the connection to the main line. It is a short piece of pipe with a lateral outlet. Pipe Tee is used to connect pipelines with a pipe at a right angle with the line. Pipe Tees are widely used as pipe fittings.