Re: whats the legal blade length?
I don't give free legal advice, especially on a public forum, and I am not your lawyer, but here are some things you may want to consider:
Knives in general
The general concealed weapon law, MCL §750.227(1), makes it a felony to carry a “dagger, dirk, stiletto, double-edged non-folding 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 or whether concealed or otherwise in a motor vehicle operated or occupied by the person, except in his or her dwelling house, place of business, or on land possessed by the person.”
Automatic Knives
MCL §750.226(a) provides that “Any person who shall sell or offer to sell, or any person who shall have in his possession any knife having the appearance of a pocket knife, the blade or blades of which can be opened by the flick of a button, pressure on a handle or other mechanical contrivance shall be guilty of a misdemeanor [not to exceed one year in jail]”
Carrying a Knife “With Intent”
MCL §750.226 provides that “Any person who, <span style="text-decoration: underline">with intent to use the same unlawfully against the person of another</span>, goes armed with a pistol or other firearm or dagger, dirk, razor, stiletto, <span style="text-decoration: underline">or knife having a blade over 3 inches in length</span>, or any other dangerous or deadly weapon or instrument, shall be guilty of a [five year] felony...”
The previous three paragraphs make up the bulk of what is a very tricky and misunderstood area of the law in Michigan.
Now look up the definition of “dangerous weapon": It specifically includes the word “knife.” Ask yourself whether that is all a police officer would need to know to arrest you for the felony of carrying a concealed weapon after finding one on you subsequent to a search. Ask yourself also whether the same would apply to any knife found concealed on or about your person, or whether concealed or not, in a motor vehicle.
Some people may tell you that it is legal to carry a knife concealed in Michigan provided that it is not an automatic knife and that it is a pocket-style knife, not designed or customarily used as a weapon.
OK, let's say your 3 1/2"-bladed 'pocket knife' was not designed, manufactured or marketed as a fighting knife, is not used as a weapon, and you do not intend to use it as a weapon. Is it legal?
What if it is an Emerson 'Commander' pocket knife? How is that knife, or that kind of knife, used, generally worn, or marketed? Still legal?
What about if your 'utility' or 'pocket knife' is ever <span style="text-decoration: underline">used</span> as a weapon? Does it then become a 'dangerous weapon' because you used it to protect yourself? What about if you only intended to carry it for the purpose of protecting yourself - maybe you told someone that is why you carry it - but you never used it for that purpose? Is it then a weapon?
If you have reason to arm yourself, for the purpose of self-protection, would it make better sense to get training, get a permit, and lawfully carry a concealed firearm?