Restrain part of hand that is a bit redundant (5,5)
I believe the answer is:
check digit
'hand that is a bit redundant' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'restrain part' is the wordplay.
'restrain' becomes 'check' (synonyms).
'part' becomes 'digit' (digit is a kind of part).
'check'+'digit'='CHECK DIGIT'
'of' is the link.
Can you help me to learn more?
(Another definition for check digit that I've seen is " redundant element".)