Shaken 車剣 are literally "wheel-swords", more commonly known as 'ninja stars'.

These weapons are part of the Shuriken family 手裏剣 means "blade hidden in the hand".
It is a traditional Japanese weapon that was particularly used in Ninjutsu under the name Shuriken Jutsu.
Many traditional schools like the Katori Shinto Ryu also use Shuriken, but in the form of small straight sticks called "Bo Shuriken".
Shuriken were used to divert attention, hurt an opponent, or as a tool. It was used by throwing to reach a target remotely but also for body to body fighting in using blunt tips.

Here we offer 5 models of Shaken 'Made In Japan' for throwing training :

3 Branch Model: 44g Weight / 10 cm Diameter / 3mm Thickness
4 Branch Model: 46g Weight / 8 cm Diameter / 3mm Thickness
Model 4 curved branches: Weight 44g / Diameter 10 cm / 3mm Thickness
6 Branch Model: 48g Weight / 8.4 cm Diameter / 3mm Thickness
8 Branch Model: 56g Weight / 8 cm Diameter / 3mm Thickness

Caution: If using as a throwing item, please ensure that no one is on the trajectory or behind the target. For the target, please use soft materials such as cardboard or cork to avoid bounces on you.