Helical Gears is made as advanced gear more than Spur Gears. Spur Gears has the the limitations of the teeths to the axis of alternation. Helical Gear has curve of the gear. The tooth shape of Helical Gear is a fragment of a twist. Helical Gears are meshed with the shafts when they are in parallel position to each other. It can e changed when the shafts are in non-parallel position. This type of configuration is known as "Skew Gears".