In most sizes of pipe, Schedule 40 corresponds to which type of wall thickness?

Schedule 40 pipe is classified as having a "standard" wall thickness. This designation is commonly used in various piping applications, indicating that it has a sufficient wall thickness for typical pressures and temperatures encountered in standard installations. Schedule numbers, such as 40, 80, and 10, refer to the wall thickness relative to the diameter of the pipe; Schedule 40 is designed to provide a balance between strength and weight, making it versatile for many plumbing and process applications.

While other designations like Extra Strong (XS) indicate a thicker wall meant for higher pressure applications, they do not apply to Schedule 40, which is specifically understood to mean standard thickness. The terms “threaded only” and “welded only” refer to the methods of joining pipes and do not directly relate to the classification of wall thickness, thus making those options irrelevant to the definition of Schedule 40.