Stephen Edwards, 54, of Langley Close, Golborne, pleaded guilty to using or threatening to use violence at the TSB bank in Ashton on December 22.
Wigan magistrates decided the offence was so serious that he should be given a custodial sentence, as he had used a weapon and caused "distress" to three members of staff.
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But they suspended the 16-week jail term for two years due to his "genuine remorse", lack of previous convictions and willingness to work with probation officers.
Edwards must complete 32 rehabilitation activity days in the next two years as part of the sentence.
A restraining order was imposed for two years which bans him from the bank on Gerard Street, and he was told to pay £300 in compensation.
Edwards also admitted breaching bail by failing to attend court on July 1 and was fined £50.