Hi Finnkai

Many thanks for that Brilliant research!
I think you have finally solved the mystery there.

To me, it makes no sense why the part number was not changed. mad
It has clearly cost you a penny!

Quote
the M16 1.5 metric thread size is pretty close to the old 5/8" 18 TPI UNF
That's a question beyond my capacity.
If do-able, it would be the best solution.

It may be this topic will help others.
It is a credit to your perseverance that this issue is now better understood!

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Jack