The basic form of the weapon is that of a pointed, rod-shaped baton, with two long, unsharpened projections (called yoku) attached to the handle. The very end of the handle is called the knuckle. Contrary to popular belief, the shaft of a traditional sai is not a blade.
Sai are constructed in a variety of forms. Traditional sai are round, while some reproductions have adapted an octagonal middle prong. The yoku are traditionally symmetrical, however, the Manji design developed by Taira Shinken employs oppositely facing yoku in an approximation to the Manji symbol (also known as the Swastika) from which it takes its name.
The sai's utility as a weapon is reflected in its distinctive shape. With skill, it can be used against a long sword by trapping the sword's blade in the sai's handle. If the user is skillful enough she/he may be able to fracture a blade or other weapon with the sai. There are several different ways of wielding the sai in the hands, which give it the versatility to be used both lethally and non-lethally. The sai is primarily used as a striking weapon or for short jabs into the solar plexus. The sai also has many defensive uses in blocking other weapons.
One way to hold it is by gripping the handle with all of the fingers and pinching the thumb against the joint between the handle bar and the shaft of the sai. This allows one to manipulate the sai so that it can be pressed against the forearm and also help avoid getting the thumb caught in the handle when blocking an attack. The change is made by putting pressure on the thumbs and rotating the sai around until it is facing backwards and the index finger is aligned with the handle. The sai is generally easier to handle in this position. The knuckle end is good for concentrating the force of a punch, while the long shaft can be wielded to thrust at enemies, to serve as a protection for a blow to the forearm, or to stab as one would use a common dagger.
In practice, some prefer to keep the index finger extended in alignment with the center shaft regardless of whether the knuckle end or the middle prong is exposed. The finger may be straight or slightly curled. Used in this way, the other fingers are kept on the main shaft, with the thumb supporting the handle.
The grips described above leverage the versatility of this implement as both an offensive and a defensive weapon. Both grips facilitate flipping between the point and the knuckle being exposed while the sai is held in strong grip positions.
The sai is typically used in pairs, with one in each hand. In the United States a common style is Yamanni Ryu. Five common kata are typically taught, including two kihon kata. The style includes a variety of blocks, parries, strikes, and captures against attackers from all directions and height levels. Use of the point, knuckle and central bar is emphasized, as well as rapid grip changes for multiple strikes and blocks.
The jitte is the one-pronged Japanese equivalent of the (Okinawan) sai, and was used predominantly by the Japanese police during the Edo period. It is a featured weapon in the curriculum of several Japanese Jujutsu and koryu schools.
In Hollywood, however, sai are portrayed as much more offensive weapons, being used as swords, daggers, and as throwing darts. Little play is given to striking with the knuckle. Thus, the traditionally rounded weapon is portrayed with a blade. For example, Jennifer Garner, who played the role of Elektra Natchios in the film Daredevil and its spin-off Elektra, holds them incorrectly with the index and middle finger straddling the middle prong inside the yoku. A grip with 2 or 3 fingers inside between the yoku and the middle shaft facilitates a slightly more flashy array of finger twirls; however, it eliminates certain defensive possibilities and knuckle strikes.
Gabrielle (Renee O'Connor) from Xena: Warrior Princess uses a pair of sai as her primary weapons in seasons 5 and 6. Here, Gabrielle wields the sai in a more traditional sense, favoring defensives moves and knuckle strikes over the more offensive moves. However, she does use them to cut a rope as a bladed knife would, implying that her set is bladed rather than round, at least in that episode, as all other shots of her sai show a traditional rounded shaft.
Sai feature heavily in movies: Raphael of the Teenage Mutant Ninja Turtles uses twin sai as his weapons of choice. Mileena from the Mortal Kombat series uses sai as her primary weapons. Li Mei in Mortal Kombat: Deadly Alliance, Sareena in Mortal Kombat: Tournament Edition and Khameleon in Mortal Kombat Trilogy also use sai. In the Last Bronx series, sai are also wielded by Nagi.
In the movie Bulletproof Monk, the villainess Nina uses a single black sai in her fight with Jade.
Sai also feature prominently in the two battles between Anck-Su-Namun and Nefertiri/Evie in The Mummy Returns, and also make an appearance in the hands of Keanu Reeves in The Matrix Reloaded. In the animated television series, Ronin Warriors, the character Lady Kayura uses a modified pair of sai as her weapons of choice. Whilst in the manga comics, TenTen in Naruto has many weapons including sai. She uses a sai attached to a chain. Also Kish from Tokyo Mew Mew uses a pair of sai, termed "Dragon swords". Also, Dan the TriceraRanger and Boi the TigerRanger of Kyōryū Sentai Zyuranger along with their American counterparts Billy Cranston, the Blue Ranger and Trini Kwan, the Yellow Ranger of the Mighty Morphin Power Rangers, Dan and Billy both wielded a double-ended staff, called the Tricerance in Zyuranger while its called the Power Lance in Mighty Morphin Power Rangers, which could be broken down into a pair of sai, while Boi and Trini weld daggers that resemble sai, called the Saber Daggers in Zyuranger while they are called the Power Daggers in Mighty Morphin Power Rangers. Also in Super Sentai and Power Rangers the villains Mele of Juken Sentai Gekiranger and her American counterpart Camille of Power Rangers: Jungle Fury ,when in their warrior forms, both wielded sai as their weapon of choice.