The teeth of a helical gear are set at an angle (in accordance with axis of the apparatus) and take the form of a helix. This allows the teeth to mesh gradually, starting as point contact and developing into collection contact as engagement progresses. One of the most noticeable benefits of helical gears over spur gears can be less noise, especially at medium- to high-speeds. Also, with helical gears, multiple tooth are usually in mesh, which means less load on every individual tooth. This helical gear china results in a smoother changeover of forces in one tooth to the next, so that vibrations, shock loads, and wear are reduced.
However the inclined angle of the teeth also causes sliding contact between the teeth, which creates axial forces and heat, decreasing effectiveness. These axial forces perform a significant role 
in bearing selection for helical gears. Because the bearings have to endure both radial and axial forces, helical gears need thrust or roller bearings, which are typically larger (and more costly) compared to the simple bearings used in combination with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although larger helix angles offer higher rate and smoother motion, the helix angle is typically limited by 45 degrees due to the creation of axial forces.