Central scaffolding component of the centrioles ensuring their 9-fold symmetry. Required for centrosome biogenesis and duplication (By similarity). Nine homodimers form a cartwheel structure with an internal diameter of 23 nM and radial spokes connecting to the microtubule triplets. Interacts with sas-5 (By similarity). Localizes to centrioles. The coiled coil domain is necessary and sufficient for interaction with sas-5. The 35 nM long coiled-coil domain mediates homodimerization while the globular N-terminus links the dimers at an angle of 40 degrees to form the inner ring.