A ring blade for cutting or for defensive purposes comprises a ring with a top section and a movable crown member mounted in this top section. The ring is adapted for placement on a person's finger. The crown member has an elongate slot formed therein and a blade member is arranged in this slot. First...http://www.google.co.uk/patents/US5301432?utm_source=gb-gplus-sharePatent US5301432 - Ring with movable blade
