In addition, the internal surface of the cylinder and {HEAD ~ the external surface} of the piston are grooved or keyed so as to prevent {TAIL ~ rotation} of the piston inside the cylinder  
are keyed to prevent
In addition , the internal surface of the cylinder and { HEAD ~ the external surface } of the piston are grooved or keyed so as to prevent { TAIL ~ rotation } of the piston inside the cylinder
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL OTH OTH REL OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH