Herringbone gears

What are Herringbone gears and what for these are used ?
In normal helical gears there is no problem of impact
stresses but there are axial thrusts on the bearings of shafts
on which they are mounted.these gears are good for
moderate power transmission because bearing can be
designed.But in very high power transmission design of
bearing for a small and compact system becomes very tough
and unemployable.Thus herringbone gears were designed to
eliminate these axial thrusts.This gear contains both right
hand helical profile and left hand helical profile on same gear
as you can see in diagram.The axial components of
transmission force is cancelled by each other on same
gear.Thus eliminating the problem of thrust force.
These gears are used in racing cars where high power
transmission is required and bearing size can not be
increased after certain limit.