Tool useful for cracking some walnuts (3)
I believe the answer is:
awl
'tool' is the definition.
(awl is a kind of tool)
'useful for cracking some walnuts' is the wordplay.
'useful for cracking' becomes 'aw' (I can't justify this - if you can you should believe this answer much more).
'some' says to take the centre.
'walnuts' becomes 'Juglans californicas' (Juglans californica is an example).
The centre of 'juglanscalifornicas' is 'l'.
'aw'+'l'='AWL'
Can you help me to learn more?
(Other definitions for awl that I've seen before include "Borer, sounds like everything" , "scribe" , "Tool for piercing holes in leather" , "What could be boring" , "Pointed tool used in leatherwork" .)