dilly-doo
an item in which the name or function is unbeknownst to (or has been forgotten by) the person uttering the term
“I twisted the dilly-doo until the thingy lined up with the whosie-whatsit and wouldn’t ya know it. The dingus got all gashnitzed and gashnizzled and the jobby-joo went wizz-bang out the back. Please forgive me if I’m getting too technical for you. It’s just that I’ve been workin’ in the doojigger biz since I was knee-high to a whatchamacallit and I rarely interact with you civilians.”