Measuring sticks (6)
I believe the answer is:
rulers
'measuring sticks' is the definition.
(ruler is a kind of measuring stick)
This is the entire clue.
(Other definitions for rulers that I've seen before include "Sovereigns and marked sticks" , "Heads of government" , "Sovereigns etc" , "Straight sticks for governors" , "Strips with straight edge to measure" .)