The tsuba is usually a round guard at the end of the grip of a Japanese sword. They contribute to the balance of the katana and to the protection of the hand. Contrary to what is commonly believed, a tsuba was mostly meant to be used to prevent the hand from sliding onto the blade during thrusts as opposed to protecting from an opponent's blade.
Tsuba can have extremely elegant shapes and are usually finely decorated, and nowadays are collectors' items. Tsuba were made by whole dynasties of craftsmen whose only job was making tsuba.