Screw driver (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
propeller
I believe this clue is a double definition.
'screw' is the first definition.
(thesaurus)
'driver' is the second definition.
(I've seen this before)
(Other definitions for propeller that I've seen before include "Screw (on a boat)" , "Driving mechanism" , "Driver" , "It rotates to push against air or water" , "Airscrew" .)