For threading metallic pipe in a gas piping installation for 1" iron pipe, what is the specified thread size?

• A. 7/8"
• B. 1"
• C. 1/2"
• D. 3/4"

Answer: (A)

In gas piping, the size labeled on the pipe (1 inch) is the nominal bore and doesn’t determine the actual thread diameter used to cut or mate fittings. For metallic gas piping, the standard thread size that’s specified for connecting with 1 inch iron pipe is seven-eighths of an inch. This distinction between nominal pipe size and the actual thread size is why the correct choice is seven-eighths of an inch. The other sizes correspond to different nominal pipe sizes and do not match the standard thread size used with a 1 inch iron pipe in gas installations.