Actors fooled, essentially, which is a wrench, perhaps (4)
I believe the answer is:
tool
'a wrench perhaps' is the definition.
(I know that spanner is a type of hand tool)
'actors fooled essentially' is the wordplay.
'actors' becomes 'to' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'essentially' indicates the central letters.
The centre of 'fooled' is 'ol'.
'to'+'ol'='TOOL'
'which is' is the link.
Can you help me to learn more?
(Other definitions for tool that I've seen before include "Cat's-paw; impress design on" , "organ" , "one of 12 [SPADES] , for example" , "Gun" , "Drive motor skilfully" .)