Fuel filter port-'73ES
 

What is the thread type/size/pitch of the original square-drive port plug that covers the in-tank fuel filter fitted over the pickup tube?

BACKGROUND: Have purchased (in Feb., 2020) a new tank from iRoll Motors (CA, USA) who gets them from VP Autoparts (USA and Sweden). These new tanks are produced in Asia and come with two plugs, neither which fits the port in the tank the way it should. (See pic of new plug.) The plugs do not engage enough threads in the tank. (VP includes a disclaimer that does not adequately address the issue.)

I believe the threads on the new tank are British Standard type.

It seems the only way to deal with this is to clean out the tank threads with a big tap or do something with the plus with a big die, but determining with certainty the threads is the first step.

CAUTION: If you are thinking of buying a new tank, ask your supplier if the problem has been solved first!