Look into the short (I think) end of the diff cup, and see if there's a hex shape cut out of the plastic.
If it's a TB-02 diff, you don't need that plastic nut holder thing.. the locknut just sits right into that space. The rest, like the spring, bearing, and screw, go on the other end. The Evo diff cups need that plastic piece since there's no nut hole, so keep it handy if you go buy the reinforced ones or something.
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