Hi and welcome to the forum.
I think from memory you must first unscrew the silver collar on the top, it will then give you access to get a spanner on the nut.
Dave.
------------- Never argue with an idiot, they will drag you down to their level and beat you on experience.
Mark Twain.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets