Failed Calibration - Plain Plug Gages - They grow!



Has anyone experienced the phenomenon of failed plain plug gauges, specificly the nogo member when the results show that the gauge has grown in size? What i'm talking about is a gauge with a .00006" tol. And the results showing the gauge to be oversize by .00002". The gauge is a class "x" and has passed calibration for the past 3 years. I call this a phenomenon because theoreticly the nogo member never enters the part being checked. I would also mention that the same outside calibration lab has preformed the calibration for the past 4 years. Can anyone shed some light on this subject for me? Any information would be appreciated.

barb butrym

Quite Involved in Discussions
Scott is it possible that the plug has been damaged in some way (ie dropped and/or burred from forcing) by mishandling? If not then I would get another opinion...could it have been cal tech dependant? perhaps the cal lab needs to be involved my guess is the correct tolerance wasn't enforced on the tool used to cal with.. for 3 years if there is no signs of mishandling? What about env conditions and the standard, at that tolerance could that have been a factor?

My guess is you will never know..... if the lab is at fault.


Barb thank you for the reply. There is always the possibility of undetectable damage. I chose to contact the lab and have the calibration preformed again by another tech.


Maybe the Lab "Soaked" the gage in a temperature higher that normal. The growth usually is caused by the steel expanding.
Just a thought.
Ron Taylor


Thanks ron,
both gauges in question have certification showing that the temp at calibration was 70 deg. I believe that should be a normal range. Past calibrations were conducted at 68 deg.


Well everyone, i received my gauges back from my cal lab. I feel the results are inconclusive. As in any measurment there is variation. The same tech calibrated the gauge this week and low and behold the results are .00007" different. The gauge passed calibration except for the go member which is still oversize. The cal temp was 3 deg different. I would presume that a go gauge could grow by material slowly wearing onto the gauge as it is passed in and out of many parts. This however still sheds no light on my original question that how can nogo members grow, not only plain plugs but also on the nogo members of thread gauges that never enter a part? This is not a new problem but a dilema that has come up time and again. Now what?


Growing Gages

Might I suggest checking a gage when first receiving it. It has been my experience that some gages are made on the high side to allow a longer life time. When I check incoming gages I also have to allow for uncertainty of the equipment that first certified the gage and then my own equipment. Hope this helps. :cool:

Charles Harvey

Inactive Registered Visitor
growing gages

I see quite a few growing gages, especially cylindrical plug gages in larger sizes. Aside from being dropped I have seen a number of oversize gages in trilock handles where the bolt is overtightened and the plug gage bellys out in the middle. The Size Control Company used to make a plug gage lapper that would help correct some of the growing gage issues.
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