Bar; eye cell (3)
I believe the answer is:
rod
I believe this is a double definition.
'bar' is the first definition.
(I've seen this in another clue)
'eye cell' is the second definition.
(I've seen this in another clue)
(Other definitions for rod that I've seen before include "Sceptre" , "Former measure equal to a quarter of a chain" , "axle" , "Spare it and spoil the child, they used to say" , "Thin straight bar" .)