{HEAD ~ The tooth shape} at around {TAIL ~ the pitch circle} of the outer tooth gear of the pinion to be connected to the prime mover or driven shaft has a tooth surface which is in axial direction at around the central portion of the tooth width and which contacts at around the tooth width end at the allowable displacement angle and the backlash is made small and the outer tooth gear of the pinion is crowned in to an exponential function curve 
at around
{ HEAD ~ The tooth shape } at around { TAIL ~ the pitch circle } of the outer tooth gear of the pinion to be connected to the prime mover or driven shaft has a tooth surface which is in axial direction at around the central portion of the tooth width and which contacts at around the tooth width end at the allowable displacement angle and the backlash is made small and the outer tooth gear of the pinion is crowned in to an exponential function curve
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