a friction element including the friction surface, said {HEAD ~ friction element} being removably supported on said base, whereby said friction element can be interchanged with other friction elements for providing {TAIL ~ respective different friction surfaces}, and said base includes a recess for removably holding said friction element 
a friction element including the friction surface , said { HEAD ~ friction element } being removably supported on said base , whereby said friction element can be interchanged with other friction elements for providing { TAIL ~ respective different friction surfaces } , and said base includes a recess for removably holding said friction element
OTH OTH OTH OTH 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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH