What tool is typically used with a hammer to cut a rounded-off nut on a vehicle?

The tool typically used with a hammer to cut a rounded-off nut is a chisel. A chisel, when struck with a hammer, can effectively cut through the material of a rounded-off nut, allowing for easier removal. This method is particularly useful because the sharp edge of the chisel can create a notch in the nut, facilitating its loosening and eventual removal from the bolt it is securing.

Using a chisel allows for precise and focused force application, which is advantageous when dealing with awkwardly shaped or damaged nuts that cannot be easily turned with standard tools. While other tools may serve specific purposes in automotive repair, the chisel is uniquely designed for this cutting and shaping task, making it the most appropriate choice for cutting a rounded-off nut.