US Patent 7086951 Nunchaku

A nunchaku includes a joint pin for connecting a baton of the nunchaku to a chain. The joint pin includes a front section for extending through a bearing mounted inside the baton to project from an inner end of the baton to connect to the chain, and a circular flange provided at a rear end of the joint pin to abut against an inner side of the bearing. The flange of the joint pin has an outer diameter larger than an inner bore of the bearing and therefore effectively prevents the whole joint pin and accordingly the chain from separating from the baton even when the steel balls of the bearing are badly worn off and fail to engage with the joint pin.