Little weight in aluminium hand tool (3)
I believe the answer is:
awl
'hand tool' is the definition.
(awl is a kind of hand tool)
'little weight in aluminium' is the wordplay.
'little' suggests taking the first letters.
'in' indicates putting letters inside.
'aluminium' becomes 'al' (Al is the chemical symbol for aluminium).
The first letter of 'weight' is 'w'.
'w' inserted inside 'al' is 'AWL'.
(Other definitions for awl that I've seen before include "scribe" , "something sharp" , "Instrument for boring holes" , "Pointed hand-tool" , "Pointed tool for making small holes" .)