Easiest way would be to use a rubber stopper.
Did you use a thread pitch gauge on the fitting?
I’m thinking it should be a standard bolt diameter and pitch (coarse or fine.)


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.