A first monoblock element is formed of a preferably circular horizontal rubbing plate including {HEAD ~ a cone frustrum} at {TAIL ~ its center} 
at
A first monoblock element is formed of a preferably circular horizontal rubbing plate including { HEAD ~ a cone frustrum } at { TAIL ~ its center }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL