Functions as part of axonemal radial spoke complexes that play an important part in the motility of sperm and cilia (PubMed:19200523). Essential for both the radial spoke head assembly and the central pair microtubule stability in ependymal motile cilia (By similarity). Required for motility of olfactory and neural cilia and for the structural integrity of ciliary axonemes in both 9+0 and 9+2 motile cilia (By similarity). {ECO:0000250|UniProtKB:Q5TYW6, ECO:0000250|UniProtKB:Q9D9V4, ECO:0000269|PubMed:19200523}. This is the function of RSPH9 (radial spoke head component 9, ENSG00000172426).