Inspection kit is redundant, but not one containing catch (8)
I believe the answer is:
otoscope
'inspection kit' is the definition.
(device for inspecting the eardrum)
'redundant but not one containing catch' is the wordplay.
'redundant' becomes 'otiose' (I've seen this before).
'but not' is a deletion indicator.
'one' becomes 'i' (roman numeral).
'containing' indicates putting letters inside.
'catch' becomes 'cop' (I've seen this before).
'otiose' with 'i' taken out is 'otose'.
'otose' enclosing 'cop' is 'OTOSCOPE'.
'is' is the link.
(Other definitions for otoscope that I've seen before include "It's used to examine the ear" , "instrument coming close to a canal" , "Device for looking in ears" , "It's used to examine 27 ac" , "Ear examiner" .)