Nunchaku

The nunchaku (ヌンチャク) 
is a traditional Okinawan martial arts weapon consisting of two sections linked by metal chain or rope.

Most widely used in martial arts such as Okinawan kobudō and karate. 
Utilized as a training weapon, since it allows the development of quicker hand movements and improves posture.

Also called nunchucks or chucks.

Attribution: Wikipedia