{HEAD ~ The hook} is disengageable from {TAIL ~ the hook anchor} only by sliding movement transverse to vertical and through the channel opening 
is disengageable from
{ HEAD ~ The hook } is disengageable from { TAIL ~ the hook anchor } only by sliding movement transverse to vertical and through the channel opening
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH