The cam plates are in contact with {TAIL ~ the cam surfaces}, and serve for positioning {HEAD ~ the sliding frames} 
The cam plates are in contact with { TAIL ~ the cam surfaces } , and serve for positioning { HEAD ~ the sliding frames }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD