Transit police followed up on a tip that "a youth was advertising fully functional brass knuckles for sale on Craigslist and selling them at points along the SkyTrain route in Surrey", said spokesperson Anne Drennan in a statement.
An undercover operation netted three sets of brass knuckles, which are listed as prohibited weapons under the Criminal Code, when the youth attempted to sell them.
A fourth set of knuckles was located at his residence, Drennan said.
Police say the teen is well known to police. He is due to appear in court on Wednesday.