Microtubule-binding protein that localizes to the microtubular manchette of elongating spermatids. Homodimer. Interacts with HOOK1. Interacts with HOOK2. Interacts with HOOK3. Localizes to the microtubular manchette of elongating spermatids. Localizes to the sperm flagella and to the basal half of motile cilia. Belongs to the CCDC181 family.