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