Helical gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions. The main reason for the popularity of spur gears is, their simplicity in design, along with being easy to manufacture and maintain. However, due to their design, spur gears create a large amount of stress on gear teeth.
Spur gears are known as slow speed gears. Spur gears are seen as noisy due to their design, so if noise is not a problem for your application, spur gears can be used at almost any speed. The noise of the spur gear occurs every time a gear tooth engages another tooth on the other gear. The teeth collide and this impact makes a noise.