A Newstead man who was found with a knuckleduster told magistrates he used it as part of his work as a sheet-metal worker.
Nigel Greensmith was stopped in his car on suspicion of drink driving, on Southwell Lane, Kirkby, at 6am on May 24, when the item was found.
Michael Little, mitigating, said the knuckleduster was made by a work-mate and was used to "de-burr" the sharp edges of metal sheets.
"People are being sent to prison for these offences, andhe is very conscious of that," Mr Little said.
When he was stopped, he was found to be under the limit. He had taken the knuckleduster home after a colleague, who made it, left the company.
"He shouldn't have done that," Mr Little added.
Greensmith, 51, of Chatsworth Terrace, admitted possessing an offensive weapon in a public place, when he appeared at Mansfield Magistrates Court, on Thursday.
He was fined £300, with £85 costs and a £30 government surcharge. The knuckleduster was forfeited and destroyed.
Here are the latest cases heard at Mansfield Magistrates Court.