As {HEAD ~ the bars} 24 rotate around {TAIL ~ a sprocket}, as shown in FIGS 4 and 5, the bars reverse direction, going from pointing up to pointing down or vice versa 
rotate around
As { HEAD ~ the bars } 24 rotate around { TAIL ~ a sprocket } , as shown in FIGS 4 and 5 , the bars reverse direction , going from pointing up to pointing down or vice versa
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL 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 OTH OTH OTH OTH