I was told you can carry a knife over 3" providing there is no criminal intent. Dearborn being an exception they have there own law.
It has been discussed several times at
http://www.migunowners.org/, PM Mr. Simmons there.
When I was under 21 I carried Fox Labs and a knife, another option is getting a flashlight like a Surefire E2D defender which has a strike bezel.
I am not a lawyer, but he is.
Here is a post by Mr Simmons.
Originally Posted by Jim Simmons
Yeah, the knives thing is a bit complicated. Unfortunately, LEOs make it more complex than it needs to be.
It's a crime to carry a pistol or other firearm or dagger, dirk, razor, stiletto, or knife having a blade over 3 inches in length, or any other dangerous or deadly weapon or instrument, if carried with the intent to use it unlawfully against another. That's one specific crime.
Then, there's the concealed weapon law which prohibits carrying a concealed dagger, dirk, stiletto, a double-edged nonfolding stabbing instrument of any length, or any other dangerous weapon, except a hunting knife adapted and carried as such, concealed on or about his or her person.
For over 50 years, LEOs have tried to merge the 3 inch rule of the first law onto the concealed weapon law. The problem is that unless a folding knife is double-edged, or a "switchblade," covered in yet another statute, then a knife isn't prohibited by this law, even if the blade is longer than three inches.
But cops keep arresting people for carrying knives over three inches in length. And the defendant keep being "offered" a plea to a misdemeanor, or a suspended sentence, or an under advisement deal if they don't contest the charge. And a lot of lawyers aren't completely up to speed on this little nuance of knife law.
And then there are cities like Dearborn that have their own knife ordinance. As I read Dearborn's ordinance, I don't see how someone can buy a set of kitchen knives and take them home in that city. Each ordinance is different, and you need to be careful with each of them.
Bottom line: except where local ordinances prohibit their carry, it is legal to carry a folding knife with a blade longer than 3 inches, as long as you don't intend to use it unlawfully against another person. However, it will likely get you arrested.