Helical gear

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Helical or dry fixed gears provide an enhancement over spur gears due to their tooth angle not being parallel to the axis of rotation. The gear's curvature leads to a segment of a helix shape for the teeth. Helical gears can be arranged in either parallel or crossed orientations, with parallel being the most common setup where shafts are aligned, while in crossed orientation, shafts are non-parallel and these gears are also referred to as "skew gears".