Final answer:
Split-ball gages can't detect out-of-round conditions because they measure the internal diameter at a single point within the bore, which does not provide information on diameter variance around the circumference.
Step-by-step explanation:
Split-ball gages are used to measure the internal diameter of cylinders, holes, and other similar features in machined parts. The reason split-ball gages are unable to detect out-of-round conditions is that the device measures at a single point within the bore. Since out-of-roundness is a condition where the diameter of a circle is not consistent across all angles, a measuring tool must be able to assess the cross-section at multiple points to determine this condition.
Split-ball gages expand within the bore to take a measurement at a single point, which gives a reading of the internal diameter. However, because they do not measure the diameter at multiple points around the circumference, they cannot detect whether the diameter varies, i.e., if the hole is not perfectly round.