Ninja Hidden Weapons are often transformed from farm tools, daily necessities, garden tools, etc. Most of these weapons were invented and designed by ninja, and only they knew how to use them. Therefore, in the eyes of others, it was no different from ordinary daily necessities.
This weapon must be worn on the fingers, so it looks like rings in a certain degree, especially for single finger knuckle duster. But it is actually made of metal, such as brass or stainless steel, so when the user wears it on his hand to attack, it is very powerful.