a clasp lower part having {HEAD ~ a dish shaped cross section} to provide {TAIL ~ a lower surface} and an open top side with upwardly facing edges 
to provide
a clasp lower part having { HEAD ~ a dish shaped cross section } to provide { TAIL ~ a lower surface } and an open top side with upwardly facing edges
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH