Central scaffolding component of the centrioles ensuring their 9-fold symmetry (PubMed:15572125). Required for centrosome biogenesis and duplication (PubMed:15665853, PubMed:19081077). 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. Localizes to centrioles, zyg-1 and sas-5 are required for centriole localization. Recruited to centrioles at the onset of the centrosome duplication cycle, then associates with the emerging daughter centriole. 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. RNAi-mediated knockdown results in failed centrosome duplication in embryos.