Fixed blades of any length are ILLEGAL to carry in Michigan unless for hunting activity. Fixed blade knives in Michigan are considered to be a dagger.
Folding blades of 3 inches or longer are LEGAL so long as you don't intend to use it against another human being illegally.
If you want to carry a knife in Michigan, you can only carry a folding knife. Fixed blades in 99% of circumstances (save for hunting) are illegal no matter the length.