Hand tool Mike found in sleeveless jacket (6)
I believe the answer is:
gimlet
'hand tool' is the definition.
(I know that gimlet is a type of hand tool)
'mike found in sleeveless jacket' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'found in' is an insertion indicator.
'sleeveless jacket' becomes 'gilet' (a gilet is a sleeveless jacket).
'm' inserted within 'gilet' is 'GIMLET'.
(Other definitions for gimlet that I've seen before include "Something for boring; cocktail" , "Hole borer" , "Small hand tool - cocktail of vodka or gin with lime juice" , "Hole-boring tool" , "Small tool for boring holes" .)