sentences: )Specification 5C3 of the American Petroleum Institute standardizes 14 casing sizes from to outside diameter ("OD").This and related API documents also promulgate standards for the threaded end finish, the wall thickness (several are available in each size to satisfy various design parameters, and in fact are indirectly specified by standardized nominal weights per linear foot; thicker pipe obviously being heavier), and the strength and certain chemical characteristics of the steel material.