There are 13 accuracy classes of gears, arranged from low to high in order of 0-12. Level 0 is the highest, level 12 is the lowest. The selection of the gear accuracy level shall be based on the purpose of the gearbox, the conditions of use, the power of the gearbox, the speed of the circle, the performance index or other technical requirements. Table 13 shows the accuracy levels for gears used in different mechanical drives. Table 14 recommends gear cutting methods and application ranges for 5-9 grade precision gear. The following figure shows the accuracy levels of gears used for different mechanical drives: