thingamajig
noun /ˈθɪŋəmədʒɪɡ/
  /ˈθɪŋəmədʒɪɡ/
(also thingamabob 
 (informal) /ˈθɪŋəməbɒb/
  /ˈθɪŋəməbɑːb/
, thingummy, thingy)- used to refer to a thing whose name you do not know or have forgotten, or which you do not want to mention
- It's one of those thingamajigs for keeping papers together.