I think you can have one as long as its not bigger then the width of your hand or so my son is telling me
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That’s not entirely accurate. Your hand has nothing to do with it. It’s the hand of the cop that matters. Cops are taught to judge a knife to be illegal if the “edge” is longer than their palm is wide. So if your hands are bigger than the cops hands, you could be in trouble.
Not all cities use that rule though. Some say 4 inches is the limit.