When two parallel and coplaner shafts are connected by gears having teeth parallel to the axis of the shaft called spur gears, the arrangement is known as spur gearing.

Another name given to the spur gearing is helical gearing in which the teeth are inclined to the axis of the shaft. There are single and double helical gears. The double helical gears are known as herringbone gears.

When two non-parallel or intersecting, but coplaner shafts are connected by gears, then these gears are called bevel gears and the arrangement is known as bevel gearing. The bevel gears, like spur gears, may also have their teeth inclined to the face of the bevel, in which case they are known as helical bevel gears.