Spur gears, also known as straight-cut gears, are a common type of gear used in a wide range of applications. They are designed to transmit large amounts of power by placing them on parallel shafts which rotate in opposite directions.
Spur gears consist of a cylinder with teeth around the outer edge. They have a straight tooth, involute profile which project radially and are parallel to the rotation of the axis. This allows for a smoother operation between each gear and permits greater mounting distances. Spur gears can have a central hub or be hubless and are available in a variety of pitch, hub and bore diameters. The standard pressure angles in spur gears are 14.5, 20 and 25 degrees, and refer to the angle that force is transmitted between the meshing gears.Spur gears are capable of meshing with other gears, with many gears being used to create large gear reductions. When they are meshed the gear with the most teeth is referred to as the gear, whereas the one with smaller teeth is referred to as the pinion. The size of the spur gear is described as "module".