Are these illegal in Michigan?

So I want to order "butterfly knives" and I want to know if they are illegal. Let me specify: Are they illegal in MICHIGAN. Its about a 3 1/2 inch "blade" even though its just a 5 millimeter thick piece of metal (flat on ALL edges). Are these illegal? i don't think so, because its technically not even a blade, but... please give me some info, and PLEASE don't say that you don't know to get more posts, because that really makes me mad...