Thread Gauge Usage
1. Inspection of parallel internal threads with plug gauges
1.1 Use of Go plug gauge
A Go thread plug gauge checks that the internal thread fits the counterpart external thread. Thus it checks that the minimum pitch diameter has been maintained, which includes the effects of pitch, flank angle and thread profile
deviations, which apparently reduce the pitch diameter. It also checks that the minimum major diameter has been maintained. This gauge does not check the minor diameter of the internal thread.
It must be possible to screw a Go thread plug gauge manually into the entire length of the internal thread without the application of appreciable force. If this proves impossible, the internal thread does not satisfy the requirements.
1.2 Use of No Go plug gauge (with red ring)
A No Go thread plug gauge checks that the specified maximum pitch diameter has not been exceeded.
It must not be possible to screw the No Go plug gauge manually into the internal thread more than two turns from either side without the application of appreciable force. If the gauge can be screwed in more than two turns, the internal thread does not satisfy the requirements.
2. Inspection of parallel external threads with Go and No Go ring gauges
2.1 Use of Go thread ring gauge
A Go thread ring gauge checks that the external thread fits the counterpart internal thread, i.e. it checks the pitch diameter, which includes the effects of pitch, flank angle and thread profile deviations, which apparently increase
the pitch diameter. It also checks that the maximum minor diameter has not been exceeded. This gauge does not check the major diameter of the thread.
It must be possible to screw a Go thread ring gauge manually over the entire length of the external thread without the application of appreciable force. If this proves impossible, the internal thread does not satisfy the requirements.
2.2 Use of No Go ring gauge (with red spot)
A No Go thread ring gauge checks that the pitch diameter of the external thread is not below the minimum size. It must not be possible to screw the No Go thread ring gauge manually onto the external thread by more than two turns without the application of appreciable force. If the gauge can be screwed on by more than two turns, the external thread does not satisfy the requirements.
3. Inspection of taper threads
Examples are metric threads to DIN 158, NPT threads to ANSI B1.20.1, pipe threads to DIN 2999, ISO 7-2:1982 or ISO 7-2:2000.
3.1 Use of thread plug gauges for inspecting internal taper threads or internal parallel threads for connection to taper threads
The plug gauge has to be screwed manually into the internal thread without the application of appreciable force. For products made to customary commercial standards, the maximum permissible deviation is one turn beyond (rear step of gauge) or one turn short (front step of gauge) of the datum plane of the gauge.
If the internal thread does not reach the front step, or if it goes beyond the rear step, the internal thread does not satisfy the requirements.
3.2 Use of thread ring gauges for inspecting an external taper thread
The ring gauge has to be screwed manually onto the external thread without the application of appreciable force. For products made to customary commercial standards, the maximum permissible deviation is one turn beyond (top surface of gauge) or one turn short (lower surface of gauge) of the datum plane of the gauge.
If the external thread does not reach the lower surface or goes beyond the top surface, the external thread does not satisfy the requirements.
4. MultiCheck thread plug gauges
"MultiCheck" plug gauges enable the thread and its depth up to 4 x thread diameter to be checked simultaneously. Special versions for up to 6xD can be supplied.
Three types of MultiCheck are available with the following reading of accuracy:
MultiCheck "Scale”: 0,5mm / MultiCheck "Vernier”: 0,1 mm / MultiCheck "Digital": 0,01 mm