What tool is used to check the side clearance of piston rings?

The feeler gauge is the correct tool for checking the side clearance of piston rings because it provides a precise measurement of the gap between the piston ring and the piston groove. This measurement is crucial for ensuring that the piston rings fit correctly within the cylinder, allowing for optimal engine performance and preventing issues such as oil leakage or inadequate sealing.

Feeler gauges consist of a series of flat, thin metal blades of varying thickness that can be inserted into the gap to find the exact clearance. This method allows for accurate assessments conforming to the manufacturer's specifications for side clearance. Proper clearance is essential for the effective functioning of the engine, as it impacts the overall efficiency, wear and tear, and thermal expansion characteristics of the components involved.

While calipers, rulers, and digital micrometers can measure dimensions and gaps, they are not specifically designed for the tight tolerances and gap measurements required in checking piston ring side clearance. The precision and flexibility of feeler gauges make them the best choice for this particular task.