If it so done, the slider may be precisely positioned by merely fitting {HEAD ~ the sliders} around {TAIL ~ the narrowed portions} 
If it so done , the slider may be precisely positioned by merely fitting { HEAD ~ the sliders } around { TAIL ~ the narrowed portions }
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