In the thread gauges system,the limit type is most common.Thread of workpiece is ensured by controlling the GO and NOT GO limit.The types of limit thread gauges systems are broadly divided into ISO class and conventional JIS class.There were two different types of conventional JIS gauges,one for inspection and one for production use.

   The ISO system is simpler and does not have two types

  Gauging system for ISO class Metric,Parallel pipe (G)

• GP,GR等用手擰進螺紋，并輕松的穿過。

Screw this gauge in a worked thread by hand smoothly.GP,GR must go through over the whole length of thread.

• NP,NR等用手擰進螺紋，螺紋擰進多不超過2圈。

Screw this gauge in a worked thread by hand smoothly by hand NP,NR shall not be screwed in it more than two revolutions from either sides.

• GW,NW等用手擰進的同時，螺紋擰進多不超過一圈。

GR,NR shall not be screwed in more than one revolution from either sides when screwing this check plug smoothly.