An element of rust protection (3)
I believe the answer is:
tin
This clue could be a double definition.
'an element' is the first definition.
(I know that tin is a type of metal)
'rust protection' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'of' acts as a link.
Can you help me to learn more?
(Other definitions for tin that I've seen before include "Ready" , "Atomic number 50" , "Silver-white element often used in food containers" , "Silver-white metal, used to make cans" , "loaf of bread" .)