I have many sets of gage pins. And should use them more than I do like once in a blue moon. I will go to my drill sets and use the drill bit shanks instead. I’m not making NASA parts and it’s my hobby shop. My projects turn out just fine without the use of gage pins. But I won’t sell them, you never know.
My sets do not have brand or tolerance listed on them. They were sourced separately, the boxes are all different, the smallest ones say M-1, minus, China. The next ones just say M-2, minus. The largest set says nothing but the sizes of the pins. I have checked them with my mics, and the ones I have checked measured about -.0001 or a little less, as best as i can determine. Like I said, I use the pins and gage blocks for masters, not the mics... I also use my calibrated and certified surface plate for my master flat, and my cylinder gauge (self proving) for my 90 degree reference. None of this would be up to snuff in a metrology lab, but they keep my other precision things honest. The pin and gage sets are in great condition, and I have VPI paper in the boxes to keep them that way, and do not abuse them.One thing that I have noticed with the Asian pin gages is that they are not necessarily 2.000" long. I have some Meyer class Z pins (one grade better than class ZZ), American made and NIST traceable calibration which also deviate from the nominal 2" although with less deviation than the Asian pins.
When I first noticed this, I did a search to see if there was a spec. for pin gage length and did not turn any up.
I mention this because I have seen vendor copy where they say that pin gages are used to measure diameters and length. McMaster Carr states
"Also known as pin gauges, these are used for precision go/no-go measuring of hole sizes and depths, checking hole location and distance, and setting micrometers." Travers Tool and MSC make a similar statement. While you can use the pin to measure depth, it should not be assumed that the pin is 2"00 long. Mike it first to get the exact length.
Here is a link to Meyer that might be interesting..
http://www.meyergage.com/abcs-of-gages/