a drive for performing rotary motion at a constant gear ratio between arbitrarily located shafts that do not lie on the same plane. The starting surfaces (axoids) of the wheels in skew bevel gears are parts of rotational hyper-boloids, and they come in contact along a straight line. Either parts of hyperboloids that have been arbitrarily cut out and joined together or parts cut out of their necks are used as the starting surfaces of skew bevel gears.
Skew bevel gears are rarely used because of the complexities entailed in their manufacture. The transmission of rotary motion between shafts not lying on the same plane is usually accomplished by screw gear drives, in whose gears the parts cut out of the necks of hyperboloids are replaced by cylinders, or by hypoid drives, whose gears have truncated cones as substitutes for the hyperboloid parts.