hi rob,when you have unscrewed the hose from the shower body the bore is the internal hose diameter NOT the thread size of the nut that is a standard size you need to make sure you get the same size bore as the one you have.Take your hose to the diy store and compare it with those on the shelf, they do vary between electric showers and mixer valves.BUT THE THREADS ARE THE SAME.compare them and you will see the difference,just get one the same only longer.
chrisd
November 2008