Angles θ1b and θ2b, each defined by opposite first and second ridge planes 1b, 2b relative to diametrical planes P1, P2 respectively, are in {TAIL ~ a range} of {HEAD ~ 30° to 38°} 
Angles θ1b and θ2b , each defined by opposite first and second ridge planes 1b , 2b relative to diametrical planes P1 , P2 respectively , are in { TAIL ~ a range } of { HEAD ~ 30 ° to 38 ° }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD