based on image search on google it looks to be a diff shaft lock pin.

 

It's a lock pin (split pin, roll pin) it should be holding the spider cross shaft in place.
Turn the carrier until you have the end of cross shaft pointed to you, and look for a hole in the carrier case where this pin would go in and through the cross shaft. If you don't see it rotate the carrier 180degrees and look again.
It is possible they lost that pin when they were working with it and just put another one in. If this pin was not in place the carrier would have come apart by now.

 

It is either...

a. the missing roll pin from your spider gear shaft that a sloppy technician lost when taking apart your carrier.
b. part of the meth pipe the sloppy techinician was enjoying that was lost when taking apart your carrier.

 

The roll pin should have to be driven in. If yours fell out, you need a new pin, or the hole is too big.

 

Yea the pin was missing from my spider gears. Tried to put it back in and it went right through. Ended up having to tap out the old one from my original carrier and then drive that one in. Took some effort to get it in hopefully it stays in there now.

Thanks for the help everyone

 

Wow, that could've been bad. That's some luck, you need to go buy a lottery ticket.