At {HEAD ~ the end} of each piston, {TAIL ~ a second camming surface} is provided which engages the first camming surface 
At { HEAD ~ the end } of each piston , { TAIL ~ a second camming surface } is provided which engages the first camming surface
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH