A spring on the other end of the collette presses the collette against {HEAD ~ the shell} to produce {TAIL ~ wiping contacts} at the opening 
A spring on the other end of the collette presses the collette against { HEAD ~ the shell } to produce { TAIL ~ wiping contacts } at the opening
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH