{TAIL ~ The region} includes an acetal material portion having a thickness less than {HEAD ~ the certain overall thickness} 
{ TAIL ~ The region } includes an acetal material portion having a thickness less than { HEAD ~ the certain overall thickness }
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD