They are used for binding in a major op. especially (5)
I believe the answer is:
ropes
'they are used for binding' is the definition.
The definition suggests an adverb but the answer is not.
'in a major op especially' is the wordplay.
'in' indicates a hidden word.
'ROPES' is hidden in the letters of 'major op especially'.
Can you help me to learn more?
(Other definitions for ropes that I've seen before include "known by clued-up workers?" , "lines" , "Painters" , "Guys" , "weaker people may be on them?" .)