WHATSIT

whats ‧ it /ˈwɒtsɪt $ ˈwɑːts-, ˈwʌts-/ BrE AmE noun [countable]

[ Date: 1800-1900 ; Origin: what's it? ]

spoken a word you use when you cannot think of the word you want:

Try and undo the screw to get the whatsit off.