該量規用于管件、管用零部件、液體器械的鏈接，且不需要密封性的以機械的結合為主要目的螺紋檢查。這種量規被檢查的螺紋等級有相應的A級和B級兩個等級，通規的A級B級的尺寸是共通的，止規分為檢查用和加工用。

      The ISO standard has no specification for this item.Parallel thread (PF) are used mainly for plumbing connections,this is,equipment involving fluids.

      There are two classes,A and B.

      There are also two types of gauges.One is for inspection and the other is for 

      metal working.The GO gauge (both plug and ring) are commonly used for both 

      A and B classes