This is a simple chakra blade that the users of Susanoo are capable of creating and wielding, and just like the Susanoo itself, each particular blade is unique to the individual involved. Despite their variations, each sword is extremely effective, and as Susanoo evolves, so does the sword.
Sasuke Uchiha's Susanoo is capable of utilising a blade resembling a regular katana that is somewhat curved at the end, which is wielded by its primary left arm. Sasuke was able to use it to cut through several stone pillars with ease.
Upon first reaching its final form, Sasuke's Susanoo gained an orb made up of the black flames of Amaterasu, which Sasuke is able to manipulate into the shape of a blade. Whilst its secondary right hand holds the orb, its primary right hand wields the blade itself.
Madara Uchiha's Susanoo possessed two distinct, undulating blades, which resembled a kris. The blades were wielded by the right arm of both sides of his Susanoo in both its incomplete and complete forms. In its final, unstabilised form, the size of the blades increased dramatically and they were wielded by its primary right arm and primary left arm. Madara could also manifest one of these blades in one of Susanoo's arms whilst only surrounded by its aura.
When Madara manifested his Susanoo in its final, stabilised form, the blades became straight and more closely resembled traditional katana, complete with sheaths. Said sheaths were held with his Susanoo's secondary arms while the swords were wielded with its primary ones. Madara could use these to cut through mountains with a single swing.
Itachi Uchiha's Susanoo wielded a blade which was curved in nature and resembled a dagger or tantō rather than a sword. Itachi demonstrated the ability to manifest this blade while only forming his Susanoo's ribcage and arms, during his battle against Kabuto Yakushi. With it, he was able to cut through Kimimaro's bones, which were stated to be harder than tempered steel.