Custom gages have been in use since the first mass produced parts came out of the industrial revolution. This is because standard off-the-shelf gages may not always be the best choice for a given measurement for several reasons: they do not ensure the proper location for the check; there may be a need to make multiple checks to improve productivity; a design is needed to help eliminate operator influence; or even a complete automated gaging station is designed for lights out operation. Whatever the gaging requirement, custom gaging has been used to increase productivity at the point of manufacture for decades.
Something that has always been striking to me about custom gage design is that what is new is what is old. When it comes to custom gage design, the basic principles of metrology are the basis for a successful gage. Not much has changed in the decades since the successful “classic” standard bench ID/OD gages, snap or even air gages were introduced.