Metal nuts get twisted by centre of spanner (8)
I believe the answer is:
tungsten
'metal' is the definition.
(tungsten is a kind of metal)
'nuts get twisted by centre of spanner' is the wordplay.
'twisted' is an anagram indicator.
'by' says to put letters next to each other.
'centre of' means to look at the middle letters.
The middle letter of 'spanner' is 'n'.
'nuts'+'get'='nutsget'
'nutsget' anagrammed gives 'tungste'.
'tungste'+'n'='TUNGSTEN'
(Other definitions for tungsten that I've seen before include "Light-filament element" , "Hard malleable metal" , "Metallic element in a strangely snug tent" , "Metallic element used for lamp filaments" , "Rare metallic element" .)