I just removed the trans filter pan for a filter change. I found a plastic plunger like part in the pan. it has a 3/4 inch dia bullet shaped head on it with a o ring and about a 1 inch long 3/16 dia shaft. Any help on what this is. Thanks

 

It's a plug for the dipstick hole when the trans is shipped from the trans plant to the truck plant. Throw it away.