The Sai is a bludgeoning as well as a stabbing weapon, with prongs that are used to trap weapons. Although it can be used as a single weapon, the Sai is usually seen used in pairs. This allows for the practitioner to incorporate the teachings of Musashi's Nito Ryu- style of sword fighting. Twirling movements during form practice improves dexterity.
Before thediscoveryof the Sai on the Ryukyu Islands the Samurai in Japan had a truncheon with a single prong called the Jutte. It is very likely that the techniques taught by karate schools nowadays would employ Jutte tecniques as well, especially when the weapon is used against a sword.