The reason why spiral bevel gears have big ends and small ends is that when manufacturing spiral bevel gears, it is necessary to ensure that the root cone angle of each tooth is equal, but the number of teeth is different, even if the number of teeth is the same, there will be gears with different sizes. Therefore, in order to make the root cone angle of each tooth equal, the tooth marks must be cut into different slopes, so that the big end is thin and the small end is wide.