I have had this for a while and was wondering what it is.
It is a Propeller 4 Blade 5 Diameter with Hole for Rotor Holder - used in 71 sets, but only in 5 in the yellow color you have.
It was produced by LEGO until 1994, and would have fit on Plate 2x3 with Helicopter Rotor Holder.
Together they would have made the rotor of a helicopter, such as in 1469-1 Helicopter Polybag.
