Helical or “dry fixed” gear, is a type of gear that offers a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Each tooth has a helical or spiral form. Since the gear is curved, this angling makes the tooth shape a segment of a helix.
Helical gears can be meshed in parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as “skew gears”.
These gears can deliver higher torque since there is more number of teeth in a mesh at any given point of time. They can transmit motion between parallel or non-parallel shafts.