Tool he'd made of use to climbers (7)
I believe the answer is:
toehold
'tool he'd made of use to climbers' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'tool he'd made of' is the wordplay.
'made of' indicates anagramming the letters.
'tool'+'hed'='toolhed'
'toolhed' with letters rearranged gives 'TOEHOLD'.
Can you help me to learn more?
(Other definitions for toehold that I've seen before include "Minor position from which further progress may be made" , "Precarious footing?" , "Position of initial advantage from which further substantial progress might be made" , "Small established position" , "Advantageous position" .)