Oil cooler line bolt.
 

Does anyone know the size of the rear oil cooler bolt? Its leaking and I want to chase the threads with a tap.

I would not suggest using a tap. The metal shavings will end up in the system and potentially make their way into circulation. Leaks are typically because the crush washers should have be replaced or from the flex portion of the stock lines.

It just sounds like grime it was tough going about half way in and sounded like sand. I know its not cross threaded. Id rather use a magnet and vacuum and fix this. Even if I half to take the oil pan off. I spent to long rebuilding this engine by myself, for it to leak on me is completely unacceptable.

Jesus this family dollar add is almost just as annoying.

Oilpan has nothing to do with the rear oil cooler line.It attaches to the rear Iron.
16mm btw. front is 18mm.

Either crush copper washer or hair line crack. Mine was hair line if you remove the bolt it will not reseal, you will need oil cooler.