Definition - What does Crossover Sub mean?
A crossover sub is a mechanical part with threaded connections. It is used to connect threaded components that have different sizes or have different thread characteristics. Crossover subs are typically found in the drill string between the drill pipe and drill collars or at other points in the drill string. These parts enable drill operators to customise installations according to the circumstances they encounter in the field.
Trenchlesspedia explains Crossover Sub
Crossover subs typically provide the connection between drill pipes and collars. They are designed with a box and threads. When joining two threaded components, one end of the crossover sub is designed to match the thread pattern of one of the components to be joined and the other end of the sub is designed to match the thread pattern of the other component. Drilling rigs usually have a large variety of crossover subs and operators use them as needed to connect disparate parts.