radiator valve

[zingo1327]

My radiators have a valve marked 1 to 5 but I was wondering what the black indicator thing under the valve does.This cold weather all my radiators are set at 5 but the black indicator thing is at a diferent point on all radiators.
Thank you in advance

[heathfield]

On installation, the innards are usually rotated so that the black indicator thing can be clearly seen, and not hidden, no matter how the valve is mounted. This indicator position doesn't otherwise matter, as the valve will still operate according to the setting you choose.