Unknown Transmission part..

Hello. My brother in law has a 98 f-150. He changed the tranny fluid and filter but when he was dumping the used fluid into my oil drum this piece came out of the the drain pan. Anyone know what it is and if its critical to be in there??? Trans works normal and shifts fine but havent driven it far til we figure out what it is or if it will hurt it. Thanks!!

Oh! That is the transmission plug. When they build the transmission, they do it upside down and that is the plug for the dipstick tube to keep the fluid in the tranny. When they test it and install it, it is just sucked down in to the pan. Just toss it out, I went through the same issue with my 97 Ford F150, I went round and round trying figure out what it was and finally someone told me.