Ninja are said to have made use of weapons that could be easily concealed or disguised as common tools. Weapons commonly attributed to them included shuriken and bo. In popular folklore, ninja also used special short swords called ninja-ken (or ninja-to see below for explanation). Ninja-ken are smaller than katana but larger than wakizashi. The ninja-to was more of a utilitarian tool than a weapon. Another version of the ninja sword was the shikoro ken (saw sword). The shikoro ken was said to be used to gain entry into fortresses. The shikoro ken supposedly could also be used to cut (or saw) through opponents.
Information from Wikipedia
© Sergio Solorzano