Thread plug gauges are used for checking female threads, which determine female threads are acceptable or not. If the go end can go through the whole threads, and NOGO end can enter not more than three turns, then we can judge that the threaded parts are with fine threads, Otherwise, we can judge the threaded parts are not with fine threads. In this reason, so  GO end is far longer than NOGO end. We often mark GO as T, NOGO as Z.

Working thread plug gauges are used to checking thread holes, which can’t be used to checking same size’s ring gauges. Know the reason more detailed, please view this blog: Can same size ring gage and plug gage fit together?

Before using thread plug gauges, the measuring parts should be checked. there should be no rust, no scratches, black spots etc. the marking of plug gauges should be clear and correct.

The standard conditions for thread plug gauge measurement are: temperature is 20 ° C, and the force is 0. It is difficult to meet this requirement in actual use. In order to reduce the measurement error, try to use the thread plug gauge and the measured parts under the same temperature conditions. When measuring, the force used should be as small as possible. It is not allowed to push the thread plug gauge into the hole or push it while turning.

ISO Metric Thread Plug Gauges

ISO metric screw threads are most commonly used type of general-purpose screw thread in the word-wide. the standard class of fit is 6H, gaugestools also provide special class of fit metric thread plug gauges, fore example, 4G,4H,5G,5H,6G,7G,7H, 8G,8H. These special class plugs are not in stock, it need custom production.

United Inch Thread Plug Gauges (UN)

UN thread plug gauges have two 1B, 2B,3B three class of fit.

2B is a general purpose class of fit, if no specially mentioned, we will provide 2B plug gauge. we just have 2B UN plug gauges in stock. 3B is closer tolerance than 2B, if clients have tighter tolerance requirement, then 3B is chosen . For 3B plug gauges, we need custom production, usually we can finish production taking ten days.

ACME Thread Plug Gauges

NPT Thread Plug Gauges

BSP Thread Plug Gauges

Trapezoidal Thread Plug Gauges

There are three styles of working thread plug gauges

  • Double ended taper-lock thread plug gauge.  it is the most important general-purpose plug gauges style. we have all plug gauges in stock using this style. There are double ends with one handle. if one GO ends or NOGO ends damaged, just thread on one new GO or NOGO ends, then the plug gauges can be used again. These types of plug gauges are economic and convenient.

thread plug gauge

  • Reversible thread plug gauge. this gauge also has GO NOGO two members, when one member was damaged or worn, the gage member can be reversed.
  • Trilock thread plug gauge. This kind of plug gauge usually used on large size. (1 1/2″ or larger) , it also has GO NOGO two members, which has s bolt fastening system

When measuring, the thread plug gauge should be inserted or pulled out along the axis of the hole, and can not be declining; after plug gages inserted into the hole, and it is not allowed to rotate or shake the gauges. It is not allowed to use the thread gauge to inspect unclean work-pieces. Thread plug gauges’ application: thread plug gauge is used for comprehensive inspection of internal thread. Thread ring gauge is used for comprehensive inspection of external thread. Thread gauge inspection: standard temperature 20 °C, standard condition of measurement force is zero.  “Three-wires method” is used to measure the single pitch diameter of plug gauges, detected on the universal length measuring instrument. Pitch, thread angle, minor diameter, gap groove is detected by tool microscope.