The cylinder thread gauge (PZ) is specifically designed for gas cylinders and is suitable for inspecting conical threads used in gas cylinders. It includes cylinder thread plug gauge, cylinder thread ring gauge, cylinder smooth plug gauge, and cylinder smooth ring gauge Cone smooth plug gauge is used to check the small diameter and taper of the internal thread of the cone at the mouth of a steel cylinder. The conical smooth ring gauge is used to check the large diameter and taper of the conical external thread at the tail of the bottle valve. There are three specifications of cylinder specific thread gauges (PZ): PZ19.2, PZ27.8, and PZ39.