Have I forgotten something BIG?

[bigdon-70blazer]

I was cleaning my workspace and came upon this in a baggie, something I got from the guy who rebuilt my th 350 tranny and I can't remember but I think it was supposed to go somewhere as I put the tranny back in. I completely removed the tranny myself and delivered it to him for a complete rebuild which he did and gave me this. I FORGOT WHERE IT GOES ! An am freaking out because the engine, tranny and transfer case is tucked away back in the blazer and I am afraid I am going to have to tear it back out! The transfer case was fine and I just cleaned it off and repainted it, going to change fluid it case before roading it. Do any of you recognize this part and am I going to have to slit my wrists later? HELP!