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