1937 Pierce Arrow Radiator Drain Valve

Maybe Loctite the threads?

I DK about how it was fashioned, but is that a “tiny” pin showing in the First photo?

Overall, the assembly looks like it was originally Brazed.

As a young man, I worked in a manufacturing factory where we constructed “high pressure” vessels that were components of machines like air conditioners

After the Vessels were brazed, they were put on conveyor arrangements and run through a furnace to heat and melt the substance applied to keep them sealed and airtight.

Before painting, at the joints, the steel looked like the photos above.

Therefore, I offer the opinion that this piece had the Top put (screwed) on, the Shaft Aligned so the hole was open, the PIN put in place, and then the top-piece Brazed to the Rod.

What do you think about that idea?

Finally, I hope, Loctite is likely not an option because of the Heat-Range the engine goes through from Startup (cold) to Running Temperature (100+ degrees).   However, I could be mistaken!

Considering your response, I guess that I was wrong.  Oh well!

You might consider contacting one or more of the expertly knowledgeable people in the Society.

For instance, John Cislak is a Gentleman who is a Master of repairing / maintaining Pierce Arrow cars.

There is also, George Teebay, who is a Master of  Knowing Almost Everything Pierce Arrow.

There are also at least a dozen others who could help, but you now have a place to start.

I trust that neither of them will balk at your approaching them on the matter, and either offer you an answer, or direct you to someone who may know.

Good Luck!