A fan assembly includes a fan and a fan guard mounted on the fan to protect the fan from contamination and damage during operation. The tool comprises a bracket component that is mounted by a number of bolts to the cylinder head to be worked on. The second deceleration ratio structure uses at least the first spur gear, a first additional spur gear rotatably supported by an additional auxiliary shaft, and a second additional spur gear rotatably supported integrally with the first additional spur gear by the additional auxiliary shaft. Accordingly, a query image may be used to retrieve a video frame set.