a clasp upper part having {HEAD ~ a dish shaped cross section} to provide {TAIL ~ an upper surface} and an open underside with downwardly facing edges 
to provide
a clasp upper part having { HEAD ~ a dish shaped cross section } to provide { TAIL ~ an upper surface } and an open underside with downwardly 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