a main cylindrical member, extending in the axial direction of said {HEAD ~ housing sections}, for movably containing said {TAIL ~ housing sections}, 
for movably containing
a main cylindrical member , extending in the axial direction of said { HEAD ~ housing sections } , for movably containing said { TAIL ~ housing sections } ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH