Allen key up the middle of the tail for tightening and removing. Some
do have flats on them for fitting and removing without the allen key.
Ahh - thanks, i'm *sure* the aforementioned apprentice didn't use one
on any of the rads - just used the valve body itself to add leverage !
Which works fine except:

I wasn't arguing - just making the point that it seems to have been
done a little lax the first time :-)