Applying Mates is one of the most important techniques used to turn a “dumb” 3D geometry into a true fully featured solid model. Mates create geometric relationships between assembly components such as nozzles and shells. As you add mates, you define the allowable directions of linear or rotational motion of the components. In other words if you move one part that has other parts “Mated” to it they will move too.
The CWI automatically creates and applies Mates when importing COMPRESS or INSPECT pressure vessel and heat exchanger models.