What size diameter hanger rod is used for 5" pipe?

For a 5-inch pipe, the standard size for the hanger rod is indeed 1/2 inch in diameter. This size provides the necessary strength and support to secure the pipe while accommodating the load and any necessary movement due to thermal expansion or contraction of the piping system.

Using a 1/2-inch hanger rod allows for proper alignment and attachment to the building structure without causing excessive stress or strain on the pipe itself. It's crucial to select hanger rods that match the appropriate size specifications according to the National Fire Protection Association (NFPA) guidelines and manufacturer recommendations. This helps ensure safety and reliability in fire protection systems.

In contrast, options such as the other diameters would either be too thin to provide adequate support or too thick, resulting in potential issues with spacing and installation efficiency. Thus, the 1/2 inch diameter hanger rod is the correct choice for effectively supporting a 5-inch pipe.