A second monoblock element has {HEAD ~ the shape} of {TAIL ~ a circular cap} with a flat blind end and covers the first element so that said blind end of the concavity is in contact with the horizontal plane situated at the top of the cone frustrum, and the horizontal peripheral edge is in contact with the rubbing plate 
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A second monoblock element has { HEAD ~ the shape } of { TAIL ~ a circular cap } with a flat blind end and covers the first element so that said blind end of the concavity is in contact with the horizontal plane situated at the top of the cone frustrum , and the horizontal peripheral edge is in contact with the rubbing plate
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH