deano- what kind of rear hub do you have? no one can answer question until you tell us what kind of hub you have because you will need to buy a specific 9-tooth driver for your hub. that is, assuming you have a cassette hub.
if you have a freewheel hub, you cannot get a freewheel that small for your hub, they don't exist. the smallest you can get for a flipflop freewheel hub is 13t. if you have a regular freewheel hub, you are going to be stuck with a 16t until you buy a new hub.