[sirdarksol]

There is little argument about the source of the tonfa.
A few people claim that it is used to pound rice, but this is unlikely, since there is another implement that is used for this.
The most likely claim is that it is a mill handle. Someone realized that, when grasped by the short, perpendicular part and held with the long end laying against the arm, it would make an excellent defensive weapon. The tonfa is thick enough that it can allow a standard forearm block to deflect a sword strike.
This weapon has one of my favorite martial arts stories attached to it.
It is said that a farming village was trying to determine how to make the weapon effective. All of the woods that they used to make the handle, however, would either break or would slip free of the weapon.
Finally, a young man said that he would travel to a nearby fishing village to see if they had an answer. (This was a big deal because farmers and fishermen tended to hate each other). The farmer talked to a boatmaker in the village and was told of a wood that was tough and flexible enough to serve their needs. When he asked why the boatmaker helped, the boatmaker replied that an ancestor of his had gone to the farmers with a similar problem regarding patching a boat, and the farmers had provided an answer. He was merely returning the favor.