Final answer:
Extra Strong (XS or XH) and Schedule 80 pipes have the same wall thickness for nominal pipe sizes up to 8 inches, beyond which they differ.
Step-by-step explanation:
The question refers to the wall thickness of pipes typically used in plumbing and various engineering applications. When you compare Extra Strong (also known as Extra Heavy, abbreviated as XS or XH) and Schedule 80 pipes, they have the same wall thickness in nominal pipe sizes up to 8 inches. However, for larger pipe sizes, this is not the case, and Schedule 80 pipes may have different wall thicknesses than Extra Strong pipes. This shared dimension between the two types is only applicable within that specific range of sizes.