The go and no-go gauges for bolts and threaded rod are special measuring tools for thread inspection, and consist of two parts: the go gauge and the no-go gauge. The go gauge is mainly used to verify the maximum limit size of the thread to ensure that the thread pair has basic screw-in ability; the no-go gauge is used to control the minimum limit size of the thread to avoid excessive clearance. The two types of gauges can effectively guarantee the interchangeability requirements of the thread when used together.
System preparation is required before testing. The operator should select the go and no-go gauge of the corresponding model according to the thread specifications of the bolt to be tested (including parameters such as nominal diameter, pitch, and tooth angle), and pay special attention to distinguishing between special gauges for different standard threads such as metric and imperial. In the cleaning process, the oil, debris and burrs on the thread surface must be thoroughly removed, while maintaining the cleanliness of the measuring surface of the measuring tool. Before use, it is also necessary to visually check whether the go and no-go gauge has abnormal conditions such as wear, deformation, rust and jamming to ensure that the measuring tool is in an effective calibration state.
The inspection operation follows the principle of step-by-step verification. First, align the axis of the through gauge with the axis of the thread accurately, apply appropriate axial force and screw it in smoothly. The qualified judgment standard is that the through gauge can pass through the entire thread section without obstruction. If there is a jam or it cannot be screwed in during this process, it means that the thread diameter is too small or there is an obvious shape and position error. After completing the through gauge inspection, the stop gauge verification is immediately carried out-when the stop gauge is screwed in for no more than 2 pitches and stops, it means that the thread diameter does not exceed the maximum limit size. If the stop gauge is screwed in too much, it reflects that the thread processing size is out of tolerance.
The judgment of the inspection results is based on three typical situations: when the through gauge passes and the stop gauge is effectively limited, the thread size is judged to be qualified; if both gauges cannot be screwed in, it usually indicates that the thread size is too small or there are serious processing defects; if both gauges can pass freely, it means that the thread size exceeds the upper limit of the tolerance. These three states correspond to the judgment conclusions of qualified, scrapped due to insufficient size, and scrapped due to excessive size.
During the test, it is necessary to pay attention to the ambient temperature being controlled at the standard room temperature of 20℃±2℃ and the relative humidity being maintained in the range of 40%-60% to eliminate the measurement error caused by temperature and humidity changes. The screw-in torque should be moderate during operation, and forced screwing to cause thread damage is prohibited. As a Class A measuring instrument, the go/no-go gauge must establish a regular calibration system. It is recommended to send it to a professional organization for accuracy re-inspection every 1-6 months according to the frequency of use to ensure the effectiveness of the traceability of the measurement value.
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