Spur gears are a type of cylindrical gear, with shafts that are parallel and coplanar, and the teeth that are directly and oriented parallel to the shafts. They’re arguably the planetary gearbox simplest and most common type of gear – easy to manufacture and ideal for an array of applications.
The teeth of a spur gear have got an involute profile and 
mesh one tooth at a time. The involute form implies that spur gears only create radial forces (no axial forces), however the approach to tooth meshing causes high pressure on the gear tooth and high noise production. Due to this, spur gears are usually used for lower velocity applications, although they can be used at almost any speed.