I know of no Ohio statute that sets a maximum blade length. The key lies with either a city ordinance, or the design of the knife. Why the design? Ohio Revised Code section 2923.11(A) defines a "deadly weapon" as any instrument capable of inflicting death, and designed or specially adapted for use as a weapon, or possessed, carried, or used as a weapon. And, Ohio Revised Code section 2923.12(A) prohibits knowingly carrying or having concealed on one's person or concealed ready at hand, any deadly weapon.
I have a Swiss Army Knife with a four inch blade. No problem. It's designed as a tool, and carried as such. By the same token, I have a butterfly knife with a 3 inch blade. Problem: it's designed as a weapon.
However, beware of the local ordinances, they'll trip you up every time. Sorry, but I know of no way to research local ordinances no-line.
