Spoke in the plural? (5)
I believe the answer is:
radii
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for radii that I've seen before include "Half diameters" , "Geometrical lines" , "Spokes of a circle" , "Halves of diameters" , "Halves of diameter" .)