（1）：Different Usable Area

45 teeth is better than 72 teeth, the number of teeth is small, the force area is large, the bite area of teeth and clamps is large.

（2）：Different Scope of Use

72 teeth require a lot of material. They are usually used for import wrenches. The density of the teeth is very large, easy to verify the wrench.

（3）：Different characteristics

（3.1）Features: short gear tooth tip height coefficient 0.8, the top clearance coefficient 0.3; For short gears, large positive displacements can be used so that the minimum number of gears in the gear can be reduced (less than 17 teeth) and will not lead to tooth sharpening, edge biting, etc., but reduce the coincidences coefficient of gear meshing.

（3.2）Ratchet handle 75 teeth features: top height coefficient 1, top clearance coefficient 0.25. Determination of short gear gear method: the full tooth height is higher than the normal gear gear, and can also be checked to determine the correct tooth pair.