Momentarily, you may have a hand in it (6)
I believe the answer is:
sleeve
'hand in it' is the definition.
I know that 'hand' relates to this answer.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sleeve that I've seen before include "Record-holder" , "Tube" , "Part of a shirt - old record holder" , "It covers the arm" , "Some wear their hearts on it" .)