Thank You Doug, that is a brilliant description👍 and much appreciated

Yes thanks Redpop 😁
Seriously though folks!
Red; you push the part resembling a collet onto the motor shaft as far as you can get it.
Then the cylindrical part with the grooved face outwards.
This part is conical on the inside to clamp the collet.
Next comes the airscrew / fan.
Then screw the conical spinner on tightly and secure with the grub screw.
Cheers, Doug 😎

do you know how it's used ?

thanks for the reply 👍

I have several.
When buying a brushless motor off E Bay, these are often included in case the application is an aircraft.
Not much use for a boat as too light for ballast!

Looks like some kind of collet from a power(mini drill) nothing to do with the boat

Specifically Red,
It's the spinner adaptor for attaching model aircraft props (airscrews) to the motor.
Will come in handy if you are building a Swamp Skimmer or hovercraft 😉
I've also seen them used for attaching cooling fans to the back end of motors in boats.
cheers, Doug 😎

These are the prop driving parts that are usually included with most out-runner electric motors.