It is sometimes know as a short sword, but is closely related to a trident. It is a hand weapon with a blade between 15 and 20 inches in length with forward curving quillions, hand grip, and pommel. It is made from solid iron weighing up to 3 pounds. The Saki of the Monouchi should extend 1 to 3 inches past the elbow. The Saki can be sharp, blunted, or smoothed out.
The Sai is of the few Okinawan weapons that did not evolve from farm tools. The Sai originated in China and was brought in by traders. Often 2 or 3 Sai were carried, 1 in each hand and a third in his belt in reserve. The Sai is restricted to Okinawan-based Karate systems.
The use of the Sai requires a very high standard of training and skill. Each Sai must function in harmony with the other. Proper use of the Sai requires many years of training.
The Sai has several grips. An open Sai is when the Tsukagashira is at the heal of the palm. A closed Sai is when the Tsukagashira is at the finger tips and the Monouchi lies on the forearm. The Yoko is used for trapping and breaking of weapons.