typically about 40 ft in length, with male threads on each end that connect with short lengths of double-female threaded pipe called couplings. (Some specialty casing is manufactured in one piece with a female thread machined directly into one end.)

Specification 5C3 of the American Petroleum Institute standardizes 14 casing sizes from 4.5 in to 20 in outside diameter ("OD"). This and related API documents also set standards for the threaded end