Kubotan

The Kubotan is a self-defense keychain weapon developed by Soke Takayuki Kubota in the late 1960s, typically no more than 140 millimeters long and about 13 millimeters in diameter, roughly the size of a marker pen and usually made of a hard high-impact plastic such as Lexan. Its body carries six round grooves and a screw eye or swivel with a split ring attachment at one end for keys, and its name is a portmanteau of Kubota, its creator's surname, and baton, though it has since become a genericized trademark.