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