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