Slider 302 is moved back and forth along guide tube 304 by a chain 306 anchored to opposite ends of slider 302 and looped about sprockets 308 and 310 at {TAIL ~ opposite ends} of {HEAD ~ tube} 304 
Slider 302 is moved back and forth along guide tube 304 by a chain 306 anchored to opposite ends of slider 302 and looped about sprockets 308 and 310 at { TAIL ~ opposite ends } of { HEAD ~ tube } 304
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH