Slight uprising over length of factories (5)
I believe the answer is:
mills
'factories' is the definition.
('mill' can be a synonym of 'factory')
'slight uprising over length' is the wordplay.
'slight' becomes 'slim' ('slim' can be a synonym of 'slight'**).
'uprising' says the letters should be written backwards.
'over' is an insertion indicator.
'length' becomes 'l'.
'slim' reversed gives 'mils'.
'mils' enclosing 'l' is 'MILLS'.
'of' is the link.
(Other definitions for mills that I've seen before include "Sir John - - (films)" , "See 7" , "Machines that grind or crush" , "''Among these dark Satanic ...'' (William Blake)" , "Bomb" .)