The piston head is fitted into {TAIL ~ a cylinder} which divides the cylinder into {HEAD ~ two hydraulic or pneumatic cells} 
The piston head is fitted into { TAIL ~ a cylinder } which divides the cylinder into { HEAD ~ two hydraulic or pneumatic cells }
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD