A helical gear unit is a form-fitting , mechanical gear unit in which the shaft axes are skewed, i.e. neither parallel (as with a spur gear unit ) nor an intersection point (as with a bevel gear unit ). Unlike worm gears , where the axes are skewed and that use helical gears on both axes helical gears and have smaller ratios (up to about 1: 5). In contrast to helical gear units with parallel axes, the two gears in helical gear units can also have different helix angles.
With helical gears, the teeth slide past each other like a screw thread and thus transmit the rotary motion. Due to the point contact of the teeth and the strong sliding friction , these helical gears can only transmit low torques and show higher wear and a poorer efficiency than normal gear gears.