It enables one to get the right angle on things (3,6)
I believe the answer is:
set square
'it enables one to get' is the definition.
The definition suggests a singular noun which matches the answer.
'right angle on things' is the wordplay.
'right' becomes 'set' (setting right is a kind of righting).
'angle on things' becomes 'square' (I can't explain this - if you can you should give a lot more credence to this answer).
'set'+'square'='SET-SQUARE'
'the' is the link.
Can you help me to learn more?
(Other definitions for set square that I've seen before include "It may be used to help one draw" , "Right-angled triangular drawing instrument" , "It helps drawing" , "Right-angled triangle used by draughtsman" , "Drawing aid" .)