Abstract: Described here in the essay are the thread gauging system as specified under Standard ASME B 1.3. Also described are the measurement accuracy classes of the acceptance system for thread dimension measurement as specified under API Spec 5B(the 16th edition). The relevance between the individual thread parameters like the thread simple pitch diameter, the functional diameter, the pitch, and ovality, etc. is analyzed so as to explain the importance and the necessity of the simple pitch measurement and the ovality measurement that are the main revised contents of API Spec 5B(the 16th edition), to the oil casing and tubing thread gauging system, which provides certain guidance and advice for establishing the acceptance-measuring system for the non-standard thread dimensions of the oil tubing and casing to be used in the oil field.