NPT thread is one of the commonly used threads in industry. It is a kind of American Standard 60 ° taper pipe thread, which is divided into general seal aid pipe thread and general seal taper pipe thread.
When inspecting the NPT external thread, the ring gauge is used to test the thread. When using the ring gauge, pay attention to whether it is still valid and the tolerance grade of the thread to be tested. During inspection, first clean up the oil and impurities on the thread to be tested, and then after the ring gauge is aligned with the thread to be tested, turn the ring gauge with the big mother finger and the index finger to make it screw in until it can't screw in free state. It is determined to be qualified if there is a certain screw in but no screw out of the base plane of the ring gauge。
After the ring gauge is used, the attachments on the measuring part shall be cleaned in time and stored in the specified measuring tool box.