can anyone tell me what this is? and where it goes

[Shanosburgess]

Decided to fix my heater control valve the other day, whilst in there I found this lose by the pollen

these are on the inside (yes I tried googling the number and came up blank)
filter

I tried to find likely places but nothing obvious became apparent, it would be nice to find its home and put it back.
cheers in advance

 

[Flying Scotsman]

Its the cap that goes over the heater control valve.

 

[Shanosburgess]

cheers i will get it back on tomorrow :lol: