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 kind of cylindrical gears. Because the tooth surfaces of the gears are parallel to the axes of the installed shafts, there is absolutely no thrust force produced in the axial direction. Also, because of the simple production, these gears can be made to a high degree of precision. However, spur gears have a disadvantage for 
the reason that they easily make noise. In most cases, when two spur gears are in mesh, the gear with more the teeth is named the “equipment” and the one with small number of teeth is named the “pinion”.
The unit to indicate the sizes of spur gears is commonly 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 portion of an involute curve as the tooth profile.
Even though not really limited by spur gears, profile shifted gears are used when it is necessary to adjust the guts distance slightly or to strengthen the gear teeth. They are made by adjusting the distance between the gear cutting device Speed Gear Reducer called the hobbing device and the apparatus in the creation stage. When the change is certainly positive, the bending power of the gear increases, while a poor shift somewhat reduces the center distance. The backlash may be the play between the the teeth when two gears are meshed and is necessary for the easy rotation of gears. When the backlash is certainly too large, it leads to increased vibration and noise while the backlash that’s too small leads to tooth failure because of the lack of lubrication.
All KHK spur gears have an involute tooth shape. Basically, they are involute gears using portion of the involute curve as their tooth forms. Searching generally, the involute form is the most wide-spread gear tooth form because of, among other reasons, the capability to absorb small center distance errors, very easily made production equipment simplify manufacturing, thick roots of one’s teeth make it solid, etc. Tooth form is often described as a specification in drawing of a spur gear as indicated by the elevation of teeth. In addition to standard full depth teeth, prolonged addendum and stub tooth profiles exist.
