The driving devices act into the ring gap, and each of {HEAD ~ the driving devices} has {TAIL ~ a separate drive} 
The driving devices act into the ring gap , and each of { HEAD ~ the driving devices } has { TAIL ~ a separate drive }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL