Acts as a component of the essential kinetochore-associated Ndc80 complex, which is required for chromosome segregation and spindle checkpoint activity during meiosis and mitosis. Required for kinetochore integrity and the organization of stable microtubule binding sites in the outer plate of the kinetochore. Participates in SAC signaling that responds specifically to disruptions in spindle microtubule dynamics. The NDC80 complex synergistically enhances the affinity of the SKA1 complex for microtubules and may allow the NDC80 complex to track depolymerizing microtubules. Component of the Ndc80 complex, which is composed of Ndc80, Nuf2 and Spc25. Belongs to the SPC25 family.