What tool is used for expanding the ends of lead pipes?

The tool specifically designed for expanding the ends of lead pipes is known as a pipe expander. This tool allows users to increase the diameter of the pipe ends, enabling better fitting with other pipe components or connectors. The design of a pipe expander typically includes a tapered shape that, when inserted into the pipe and turned, gradually spreads the material, allowing it to expand evenly without causing damage.

The other options do not serve the purpose of expanding pipe ends. A turn pin generally helps to align or hold components together and does not have the capability to expand pipe ends. A hydraulic crimper is used for crimping or joining pipes, usually with the aid of hydraulic pressure, but it doesn't expand pipe ends. A punch tool is more suited for creating holes or indentations in materials rather than expanding them. Hence, the pipe expander is the correct and most appropriate tool for this task.