The teeth on helical gears are cut at an angle to the face of the apparatus. When two teeth on a helical equipment system engage, the contact begins at one end of the tooth and steadily spreads as the gears rotate, until the two teeth are in full engagement.
This gradual engagement makes helical gears operate a lot more smoothly and quietly than spur gears. For this reason, helical gears are used in virtually all car transmissions.
Due to the angle of the teeth on helical gears, they create a thrust load on the Motorbase apparatus when they mesh. Devices that use helical gears possess bearings that may support this thrust load.
One interesting thing about 
helical gears is that if the angles of the apparatus teeth are right, they can be mounted about perpendicular shafts, adjusting the rotation angle by 90 degrees.