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