Parts such as the Swingarm: Nut,8mm, Nut, Guard,chain, Arm-comp-swing,silver are included in the Ex250f15 Ninja 250r 2001 Usa California Swingarm parts fiche.
With a quantity of two pieces, the Adjuster-chain is the most used part in the SWINGARM diagram.
Check out any of the ten Swingarm components enlisted.