In this paper, we describe a range measuring method to inspect various different pistons by projecting a laser line onto the crowns. There exist a number of similar piston types with very slight differences but with the same overall diameter such that it is readily possible to fit the incorrect piston to an engine. Differences between a number of families of similar pistons are found in obvious features such as gudgeon pin diameter and position, etc. Within a family, the differences are more subtle and may be simply a change in the shape of the bowl in the crown of the piston. A vision based measurement system is designed to confirm the identity of the piston just after it has been fitted to the engine assembly.