For reasons of economy, an upper limit of {HEAD ~ 5 percent} by weight, {TAIL ~ preferably even only 4.5 percent} by weight, should not be exceeded 
For reasons of economy , an upper limit of { HEAD ~ 5 percent } by weight , { TAIL ~ preferably even only 4.5 percent } by weight , should not be exceeded
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH