As mentioned above, {HEAD ~ the distance} between {TAIL ~ the brush members} arranged in series can vary 
As mentioned above , { HEAD ~ the distance } between { TAIL ~ the brush members } arranged in series can vary
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH