The chains 17 are located at {HEAD ~ a position} lower than the level of the moving surfaces of {TAIL ~ the rollers} 13 
The chains 17 are located at { HEAD ~ a position } lower than the level of the moving surfaces of { TAIL ~ the rollers } 13
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH