OP states the NC was found in Receiving Inspection.“For the receiving inspection of mechanical components, the threads are checked with threaded ends, not with valid / calibrated thread plug (go-no/go) and this, for all sizes of threads”.
OP states they are checking to see if the supplier sent them panels with the correct threads.whether the supplier has the metal panels with the right threads
You do not need class 3A precision in this case, but I can imagine a scenario where a gauge can be worn to the point it now falsely accepts a different thread. Very major wearing, I know... but I have seen operators return completely stripped gauges.
If this is indeed a check during Incoming Inspection, it would be advisable to use the right tool for the job.
If this is actually some other kind of check you are performing, your company can pretty much make the process anything they want (like Jim said, using the corresponding bolt), but be prepared to back it up to an external auditor. This was a good internal audit. Someone brought up something that could be a possible major finding. Or it is absolutely nothing. Either way, the auditor is doing their job. Now your company has to weigh their options and address the finding.
OP, I think we could use a little more clarification on how and where in the process these "threaded ends" are being used.