What is this part?

[scubadoo48]

I would imagine there should be two of these on each end but there is only one on the rod. I need to know what it is and do you know where to purchase? Thank you in advance!

 

[Doc Sprocket]

Remove it, and throw it out. That is what is left of an inner bearing race. As these things are not meant to come apart, it's junk.