The Tiny Propeller is treasure that can be obtained in Sly Cooper: Age of Thieves in the episode In the Air Tonight. It is worth 175 coins and the time needed to get to the safehouse is twenty-eight seconds.
"This little propeller is the first of its kind, designed by Otto van Cooper himself. Seeing as it's been awhile, Otto has forgotten its original use, though he believes that it may have been a part for a boat of some kind."
It is located underneath Gustav's headquarters due to an old crumbling wall. Sly's Buccaneer Costume is the only thing that can be used to access this treasure.