Note shaped metal implements above, used in vault, for instance (8)
I believe the answer is:
keystone
'vault for instance' is the definition.
'keystone' can be an answer for 'vault' (thesaurus). I am not certain of the 'for instance' bit.
'note shaped metal implements above used in' is the wordplay.
'shaped' indicates anagramming the letters.
'metal implements above' becomes 'keys' (I can't explain this - if you can you should give a lot more credence to this answer).
'used in' means one lot of letters goes inside another.
'note' anagrammed gives 'tone'.
'tone' enclosing 'keys' is 'KEYSTONE'.
Can you help me to learn more?
(Other definitions for keystone that I've seen before include "Fundamental item in a structure" , "Chief element" , "Central block at the top of an arch" , "What tops an arch" , "Central policy; arch top" .)