wherein said extensions form bearing {HEAD ~ face portions} with front face portions and rear face portions and gaps between said bearing {TAIL ~ face portions} and respective portions of said guide face with front gap portions and rear gap portions, 
wherein said extensions form bearing { HEAD ~ face portions } with front face portions and rear face portions and gaps between said bearing { TAIL ~ face portions } and respective portions of said guide face with front gap portions and rear gap portions ,
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH