A second monoblock element has {HEAD ~ the shape} of 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 {TAIL ~ the rubbing plate} 
A second monoblock element has { HEAD ~ the shape } of 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 { TAIL ~ the rubbing plate }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD 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 OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL