Hanging file stent components (HFSC) of automotive transmission require high reliability, because the assembly quality has direct influence on the whole vehicle performance, especially in the area of security. But it is easy to make mistake in assembling it, and it is hard to detect errors, because the HFSC has many different parts, which have similar shape. This paper analyzes the geometrical features of the hardware of HFSC, and helps to find out those parts needing inspection through researching the possible mistakes. According to the results of the analysis, an automatic inspection system which is controlled by microcontrollers for HFSC quality measurement is designed. This system uses a new sensor designing according to the necessary of detection, and a suitable sensor planning program is presented. After the accomplishment of this system, it is proved flexible and effective through half year of practice.