Thanks NT. When I refitted the ring the first time I didn't realise
that a little magnetic ring fixed round a threaded bit of plastic had
to be screwed into the end of the motor shaft. I found this bit of
plastic on the floor and luckily I kept it not knowing what it was and
thinking it probably important. That now fitted it all works
perfectly.

As for the 2'ish diameter: - what I meant to say was 2'ish millimetre
diameter. Blame it on the late nights and the over consumption.

Cheers

Matt.