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What do these numbers mean?  Thread pitch (I dont think so)...inverse diameter...moon crater gauge??

I thought it would help me determine the size of a stem, but I don't think so.

When I see the answer...I know I am gonna kick myself.

2021-05-20 08_25_02-Photos.png

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It's an arbitrary system, but oddly enough it corresponds to the stem "tap sizes", where a tap 7 = 1.20mm, tap 8 is 1.10mm etc. I think they took the "tap size" from the Martin screwplates. There are different plates too, L and B are most common, with a slight difference in thread pitch, G is left hand thread (gauche in French).

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8 minutes ago, nickelsilver said:

It's an arbitrary system, but oddly enough it corresponds to the stem "tap sizes", where a tap 7 = 1.20mm, tap 8 is 1.10mm etc.

All rooted into the history of thread standardization, about which some resources are below

https://wikipedia.org/wiki/Thury_thread

https://www.chiark.greenend.org.uk/~alanb/martin.html

https://www.researchgate.net/publication/233455494_Standard_Screw_Threads_For_Scientific_Instruments_Part_I_Production_Techniques_And_The_Filiere_Suisse/link/568c0ec708ae153299b63b04/download

 

 

 

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