The fine threading of the valve stem and {HEAD ~ the larger seat area} allow for {TAIL ~ precise resistance} to flow 
The fine threading of the valve stem and { HEAD ~ the larger seat area } allow for { TAIL ~ precise resistance } to flow
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH