The length of the links? (5)
I believe the answer is:
chain
This clue is a double definition.
'the length' is the first definition.
(I've seen this before)
'the links?' is the second definition.
(a chain is made up of links)
'of' acts as a link.
(Other definitions for chain that I've seen before include "Succession" , "One kind of mail" , "Paper decoration" , "Links - sequence - 22 yards" , "Event series" .)