The horizontal spacing for supporting pipe made of cast iron should be a maximum of _____ feet.

The maximum horizontal spacing for supporting cast iron pipe is 10 feet. This standard is based on the weight and rigidity of cast iron, which requires adequate support to prevent sagging or stress on joints. Proper support spacing ensures that the pipes remain secure, minimizes the likelihood of failure, and helps to maintain system integrity. Adhering to the 10-foot spacing not only helps in distributing the weight effectively but also allows for the expansion and contraction that may occur due to temperature changes, which can be particularly important in plumbing systems. This consideration is crucial for ensuring the longevity and reliability of cast iron piping systems.