What tool is used on cast iron pipe joints to hold the hot sealing lead in the joint?

The tool used to hold the hot sealing lead in cast iron pipe joints is known as the asbestos joint runner. This specialized tool allows for the application of lead, which is melted and poured into the joint to create a seal between the pipes. The asbestos joint runner ensures that the lead is contained and helps maintain the proper shape and placement during the sealing process, preventing any leaks or weaknesses in the joint.

Utilizing the asbestos joint runner is crucial in plumbing projects involving cast iron pipes, as it contributes to the durability and reliability of the seal. The other tools mentioned, such as pipe cutters, lead pots, and soldering irons, serve different purposes in plumbing work and are not specifically designed for managing lead in cast iron pipe joints. This distinction highlights the importance of using the correct tool for the task to achieve optimal results.