Jigs are divided into two types: tooling jigs and testing jigs. The former is a tooling jig designed to facilitate processing and meet the needs of accuracy in machining, welding, assembly and other processes; the latter For testing purposes, because some mechanical dimensions are inconvenient to measure due to their complex shapes, we have to design special testing blocks or testing tools designed for a certain product. For example, we have some rules such as plug gauges and ring gauges. Inspection tools, but some are irregular, so a specially designed inspection tool must be designed. Some machining methods such as wire cutting, EDM, and CNC machining centers may be used to ensure the accuracy of the inspection tools before entering automation and CNC system machines. Later, jigs were no longer needed as tool paths were digitized and stored in memory, but "fixtures" were still commonly used.