some sort of robot dildo or a counterweight

Counterweight for a doohickey?

Keep guessing.

Butt plug !!

That's one weird ass anal canal to have threads lol

Some kind of plumbing or gas fitting?

2 hints:

1. It's an antique
2. It is from the transportation sector

An antique counterweight from a crane

Not a counterweight...your 1st guess about plumbing was a bit more congruent.

Then either an old water spout or some kind of valve, and if it's a valve, then it should have a handle on the end.