Petrol tank thread?

[SteveBorland]

Getting ready to Mount the Roadster tank, but the rear tank mounting strap threads are rather gunged up with paint and stuff. What thread are they? A 5/16 unf feels very tight….

 

[concours]

My '74 is. Chase them with a bottoming tap.

 

[SteveBorland]

Thanks, will do this tomorrow