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