The Circulating sub is a special tool for circulating drilling fluid when running in casing on the way or finishing running casing downhole. According to actual needs, there are circulating sub with casing thread and circulating sub with union thread (All sizes)
Construction
The Circulating Sub consists of upper thread that connects with drill pipe, buttress thread lower end that links with casing coupling. It is gone through the process of heat treatmentwith high quality alloy steel, and become much stronge and more reliable in use.
