Which of the following is a characteristic of a thrust bearing used in most radial engines?

The characteristic of a thrust bearing used in most radial engines being a deep-groove ball is significant because these types of bearings are designed to handle both radial and axial loads, which is essential in a radial engine's operating environment. In radial engines, the crankshaft is subjected to forces that can create axial movement, particularly due to the reaction to the combustion process.

Deep-groove ball bearings have a robust design that allows them to accommodate misalignment and still maintain effective rotation. They provide good load distribution and are capable of tolerating some degree of axial load without compromising the wear or performance. This makes them particularly suitable for applications where space is limited and precision is critical, as is often the case in aircraft engines.

The other bearing types listed may have specific applications in different contexts, but they do not adequately support the dual load requirements in radial engines as effectively as deep-groove ball bearings do.