Aikido jo practice or Jodori is using a wooden staff 4.2 feet / 127cm long and about one inch in diameter. Used either with a spear or without, it has round shape and no flat edges. Jo allows to use both ends and any possible rotation angles, thus making it more flexible in directions than bokken. Jo is practiced on both sides, right and left hand without any priority to the personal preferences. Jo is practiced both in kata, strikes and partner techniques. Also Aikido uses jo for hand-weapon practice called Aiki-Jo.
The techniques for jō were reportedly invented by Musō Gonnosuke Katsuyoshi (夢想 權之助 勝吉, fl. c.1605, date of death unknown) after he was defeated by the famous swordsman, Miyamoto Musashi (宮本 武蔵, 1584–1645). They fought each other in a duel sometime between 1608 and 1611, according to Kenji Tokitsu. The record mentioning this duel, the Nitenki, recounts:
When Musashi was in Edo, he met an adept named Musō Gonnosuke, who asked to fight him. Gonnosuke used a wooden sword. Musashi was in the process of making a small Bo; he picked up a piece of firewood. Gonnosuke attacked him without even bowing, but he received a blow from Musashi that made him fall down. He was impressed and left.