The historical Japanese samurai had many training tools in their martial arts skills.
Some like the sword and spear were suited for direct battlefield warfare, while others like the jutte, kusari fund, and tessen were used more day to day.
The tesson (iron war fan) was one of these personal training tools.
In the day-to-day dress of the samurai, the fan was a popular item. Traditionally made out of bamboo and paper it was the type of item one could carry anywhere.
One such version of this tool has the wooden parts replaced with metal, turning it into a short club.
Evolving from this was the war version which is a small iron bar in the shape of a closed fan.
Training with the tessen has some specific skills attributed to it like ken kudaki, in addition to is being used to amplify locks and restraints found in jujutsu.
An interesting and dynamic historical training tool in the martial arts.