A standard spare part is simply capital (5)
I believe the answer is:
paris
'simply capital' is the definition.
'Paris' can be an answer for 'capital' (capital of France). I'm not certain of the 'simply' bit.
'a standard spare part' is the wordplay.
'a standard' becomes 'par' (standard of play in golf).
'spare part' becomes 'is' (I can't explain this - if you can you should give a lot more credence to this answer).
'par'+'is'='PARIS'
'is' is the link.
Can you help me to learn more?
(Other definitions for paris that I've seen before include "French city" , "City where one may see the Mona Lisa" , "French department" , "I spar (anag)" , "French capital - Trojan prince" .)