Which type of gears are typically used when two shafts operate in parallel?

The correct answer is herringbone gears. Herringbone gears are unique because they combine the features of both helical and spur gears, allowing them to effectively handle parallel shafts. These gears consist of two helical gear sets that are arranged in a V-shape, which helps to eliminate axial thrust forces typically produced in helical gears. This design not only allows for smooth and quiet operation but also enables efficient power transmission between parallel shafts.

When considering other gear types:

• Helical gears can be used for parallel shafts, but they do create axial thrust, which needs to be managed.

• Spur gears are commonly used for parallel shafts and provide a simple and efficient connection; however, they lack the smooth operation and load capacity of herringbone gears.

• Bevel gears are primarily designed for shafts that are oriented at angles to each other, typically at 90 degrees, making them unsuitable for applications involving parallel operation.

Thus, herringbone gears stand out for their ability to efficiently connect parallel shafts without the disadvantages associated with thrust and can handle higher loads than the alternatives.