---I have these two older gauges along with these photos and short stories
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Sunnen AG300 differences
---here's two different old AG300 gauges.
---the older one has only one hole choice at the bottom of the spring---and the other one has two choices and has the spring in the second choice
---older AG300 gauge inside front of right side gauge serial #18567
---notice that the top of the springs are mounted different
---this spring is tilted further inward at the top
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--both of these AG300's are too old to accept Sunnen standard/medium & large point sets listed in the 2017 Goodson catalog
---I have built my own gauge points sets using brass hex pieces and pressed in the balls
---gauge point sets cost like $55 to $77 for each set in the 2017 Goodson catalog
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---just a photo of my 2 AG300 gauges
---this flat piece of piece tin has all the various sizes engraved on it so I don't have to go looking next time
-------------------------------------------------------------------------------------this is the new gauge I bought
---this link shows how to use and set up the Sunnen AG300 gauges
https://www.sunnen.com/graphics/assets/documents/e7589cbe80c6.pdf
--I haven't looked at this sunnen link for a long time but you might be able to find something in there
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---this serial #21374 AG300 is not quite as old---and has two choices for the spring which is mounted in the second choice
---top of this spring is moved up and to the right some
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---these Sunnen AG300's new in 2021 cost----------------$4220 each---have these two
---#213Y4 has a new .0001” white gauge
----#18567 has an old .0001” red /green gauge
