One of the strips is then turned end to end without rotation, so that {HEAD ~ both faces} on {TAIL ~ the upper surface} are either inner faces or outer faces 
on
One of the strips is then turned end to end without rotation , so that { HEAD ~ both faces } on { TAIL ~ the upper surface } are either inner faces or outer faces
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH