Enlarging holes in frame

[Chamberpains]

I don't know if you'll find exactly what your looking for. You may have to adapt to the size line your running. But search "bulkhead fittings" thats the type of fitting that your showing in the picture you posted.

**edit**

I didn't see the OP had called it a bulkhead fitting in his original post. I'll leave my original post for a redundancy. But I did find what us called a "thru hull" fitting. That may be long enough but doesn't come with threads inside. You can easily get what ever NPT (national pipe thread) tap size you need and cut threads and adapter reduce it down to what you need.