Roller 60 is movable along a surface 62 of {HEAD ~ the front section} 11b of {TAIL ~ the fixed frame} 11 
of
Roller 60 is movable along a surface 62 of { HEAD ~ the front section } 11b of { TAIL ~ the fixed frame } 11
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH