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