Spur gears are the most easily visualized common gears that transmit movement between two parallel shafts. Because of the shape, they are classified as a type of cylindrical gears. Because the tooth surfaces of the gears are parallel to the axes of the mounted shafts, there is absolutely no thrust force generated in the axial path. Also, because of the ease of production, these gears can be made to a high degree of precision. However, spur gears possess a disadvantage for the reason that they very easily make noise. In most cases, when two spur gears are in mesh, the apparatus with more teeth is called the “gear” and the one with small number of the teeth is named the “pinion”.
The unit to indicate the sizes of spur gears is often stated, as specified by ISO, to be “module”. In recent years, it is typical to create the pressure angle to 20 degrees. In commercial machinery, it is most common to use a part of an involute curve as the tooth profile.
Even though not limited by spur gears, profile shifted gears 
are utilized when it is necessary to adjust the center distance slightly or even to strengthen the gear teeth. They are made by adjusting the distance between your gear cutting device called the hobbing tool and the apparatus in the production stage. When the shift is definitely positive, the bending strength of the apparatus increases, while a negative shift slightly reduces the guts distance. The backlash is the play between the the teeth when two gears are meshed and is needed for the easy rotation of gears. When the backlash is definitely too large, it leads to Cast Iron improved vibration and noise while the backlash that is too little leads to tooth failing due to the lack of lubrication.
All KHK spur gears possess an involute tooth form. Basically, they are involute gears using area of the involute curve as their tooth forms. Looking generally, the involute shape is the most wide-spread gear tooth form due to, among other factors, the ability to absorb small center distance errors, very easily made production tools simplify manufacturing, thick roots of the teeth make it strong, etc. Tooth shape is often described as a specification in drawing of a spur equipment as indicated by the height of teeth. Furthermore to standard complete depth teeth, extended addendum and stub tooth profiles exist.