A spur gear is a cylindrical gear whose tooth line is a straight generatrix of an indexing cylindrical surface. Its tooth ribs are parallel to the straight line of the shaft center.The characteristic of spur gear transmission is that the axes of the large and small gears are parallel to each other, and the two gears rotate in opposite directions when externally meshing.And spur gears have good manufacturability, easy to ensure accuracy, and are the most widely used.