The slider has {HEAD ~ a contact portion} in {TAIL ~ close contact} with the inner peripheral wall and positioned upstream of the block member at the first position in the sliding direction 
The slider has { HEAD ~ a contact portion } in { TAIL ~ close contact } with the inner peripheral wall and positioned upstream of the block member at the first position in the sliding direction
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH