Extremely brittle part of wheel, tailor-made (7)
I believe the answer is:
bespoke
'tailor-made' is the definition.
(synonyms)
'extremely brittle part of wheel' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'part of wheel' becomes 'spoke' ('spoke' is part of 'wheel').
'brittle' with its centre taken out is 'be'.
'be'+'spoke'='BESPOKE'
(Other definitions for bespoke that I've seen before include "Made to measure" , "Of clothes, made to order" , "Tailor-made" , "Description of tailor" , "Custom-made" .)