{HEAD ~ an indicator means} rigidly affixed to the swing arm for visually indicating the variation of the thickness of a brake block from {TAIL ~ a specified thickness} 
{ HEAD ~ an indicator means } rigidly affixed to the swing arm for visually indicating the variation of the thickness of a brake block from { TAIL ~ a specified thickness }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL