Thanks for the tips, yes I mean the lock nut on the top of the damper. I have removed the tension on the spring in order to gain access to the locknut. I suppose I wasn't expecting to do this job as other blogs make no mention of having to fit the brass extender, which makes me think it should have been done before delivery. Ok, I probably just lack some confidence here (also don't have a desk vice, so I am using workmate bench for vice)