78 fuel inlet on carb inlet

The aftermarket version of the filter fitting that I found was not bigger and self-tapping but only longer and could go in and still capture unused threads internally. As previously stated, the threads are not the seal but the nylon washer on the end is the gasket and it provides the seal.

Ok, we removed carb

And screwed in fitting very 

Carefully and it went in correctly and no leaks. 

Thanks for the info evryone!