It is furthermore of advantage for the inner thread to have an inner diameter that diminishes with increasing distance from {HEAD ~ the free end} of {TAIL ~ the cap} towards its interior 
It is furthermore of advantage for the inner thread to have an inner diameter that diminishes with increasing distance from { HEAD ~ the free end } of { TAIL ~ the cap } towards its interior
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH