OCTG divided into oil casing and oil tubing.

Casing is a large-diameter pipe that serves as the structural retainer for the walls of oil and gas wells, or wellbore. It is inserted into a well bore and cemented in place to protect both subsurface formations and the wellbore from collapsing and to allow drilling fluid to circulate and extraction to take place.

The outer diameter generally is 4-1/2"to 13-3/8"

Model:	API 5CT
Trademark:	Gr steel pipe