A feature of the invention relates to the material used on the contacting surfaces of {TAIL ~ the base member} and {HEAD ~ the flaps} 
A feature of the invention relates to the material used on the contacting surfaces of { TAIL ~ the base member } and { HEAD ~ the flaps }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD