On helical gears the teeth are cut at an angle to the axis of the gear. As the line of contact on a helical tooth is not parallel to the axis, tooth contact and loading is gradual and is highly advantageous at higher speeds when spur gears are not practical.
Helical is the most commonly used gear in transmissions. They also generate large amounts of thrust and use bearings to help support the thrust load. Helical gears can be used to adjust the rotation angle by 90 deg. when mounted on perpendicular shafts.
Helical Gears have teeth that are set on an angle to the gear axis. Since the teeth engage more gradually, they have a smoother and quieter operation than spur gears. Helical gears also have greater tooth strength and a higher load carrying capacity.