I have always found a fairly standard (draper I think ) sockett, even on no 3, I agree on using fingers to screw plugs in rather than a socketts and just use a extension bar to grip with my fingers. On engines I have worked on before I often use box spanners as they are cheap and I know the plugs are not going to be gorrilla tight, plus a roll of box spanners lives on the bike so is convienient, and only £10 for a full set they are cheap enough to live on the bike as a pernament tool set without worrying about loss or rust.