This one is going to be harder... lets see. A bolt would be too obvious, and the threads are squared. Looks like a bit of rust on the left middle. The top half down to where the rust starts most likely goes in and out of what ever it is attached to which is why it looks cleaner.
If I had to guess its part of some sort of shop tool like a bench drill.
Maybe you folks that *know* about machined threads can look at one and say what it goes to, but to me, this is like posting a photo of a button and asking what article of clothing it would be sewn onto!