Geometrical instruments used for making walking aids (9)
I believe the answer is:
callipers
'geometrical instruments' is the definition.
'callipers' can be an answer for 'instruments' (calliper is a kind of instrument). I am unsure of the 'geometrical' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for callipers that I've seen before include "measuring instrument" , "They can't work without legs" .)