Which tool would be used along with a hammer to cut a rounded-off nut on a vehicle?

Using a chisel in conjunction with a hammer is the appropriate choice for cutting through a rounded-off nut on a vehicle. A chisel, typically made of hardened metal, can be employed to create a groove or notch in the nut’s surface. By aligning the chisel at an angle and striking it with a hammer, the technician can effectively break the bond of the nut and allow for easier removal.

This method is especially advantageous when the nut has been stripped or rounded off, making conventional tools ineffective. The chisel can be used to chip away metal around the nut or even cut into the nut itself, thereby loosening it enough for removal.

Other tools mentioned, such as files, punches, or screwdrivers, serve different purposes. A file is primarily used for smoothing surfaces and wouldn’t be effective for cutting through metal. A punch can create indentations or align holes but is not suitable for cutting or applying enough force to loosen a tightly fastened nut. A screwdriver is designed for turning screws and wouldn't provide the necessary cutting action or impact force needed in this scenario. Thus, the use of a chisel with a hammer is the most effective approach for dealing with a rounded-off nut.