These have to be instrumental in forming wheels (6)
I believe the answer is:
spokes
'wheels' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe they are linked in a way I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for spokes that I've seen before include "Parts of a wheel" , "Radial supports on a wheel" , "Radials of a wheel" , "Bicycle wheel struts" .)