wherein said slide faces and piston shoes have {HEAD ~ a pair} of extensions at opposite ends of {TAIL ~ said medial portions} in the direction of the movements of said piston shoes, 
wherein said slide faces and piston shoes have { HEAD ~ a pair } of extensions at opposite ends of { TAIL ~ said medial portions } in the direction of the movements of said piston shoes ,
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH