What does a dial bore gauge identify in a cylinder?

A dial bore gauge is specifically designed to measure the internal dimensions of a cylinder, primarily focusing on its diameter. It allows for precise measurements at different points within the cylinder to determine whether the diameter remains consistent throughout its length.

When it comes to identifying taper, the dial bore gauge is particularly effective. Taper refers to a condition where the diameter of the cylinder varies along its length, meaning that one end of the cylinder may be wider than the other. The gauge's ability to measure at various heights within the bore enables the technician to detect any taper condition, indicating not just a simple failure of roundness but a broader problem that can impact engine performance.

While the other options touch upon aspects of measurement that can be relevant in certain contexts, they don’t align with the primary function of a dial bore gauge. Protrusion, length, and diameter can all be elements associated with measuring a cylinder, but the dial bore gauge excels at identifying taper specifically, making it crucial in evaluating the engine's internal condition for maintenance or repair decisions.