Here, {HEAD ~ brush member 4 a} is spaced apart from {TAIL ~ brush member} 4 b 
is spaced apart from
Here , { HEAD ~ brush member 4 a } is spaced apart from { TAIL ~ brush member } 4 b
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH