Spoke of part of arm (6)
I believe the answer is:
I believe this clue is a double definition.
'spoke' is the first definition.
'part of arm' is the second definition.
(I know that radius part of forearm)
'of' is the link.
(Other definitions for radius that I've seen before include "Human forearm bone" , "Centre-circumference length" , "It runs from the centre to the circumference" , "from centre to boundary" , "Outer arm bone" .)