a hub half forming the support body and {HEAD ~ the hub halves} collectively defining {TAIL ~ an interior space}, 
collectively defining
a hub half forming the support body and { HEAD ~ the hub halves } collectively defining { TAIL ~ an interior space } ,
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH