Schedule 40 pipe and 304 stainless steel are two different aspects of piping and material specification:

Schedule 40 Pipe: 

Schedule 40 is a designation used in the American National Standards Institute (ANSI) to classify the thickness and pressure rating of pipes. It is a common standard for pipes made from various materials, including metals and plastics. In the case of metal pipes, such as steel or stainless steel, Schedule 40 indicates a specific wall thickness.

Schedule 40 pipes have a relatively thick wall compared to Schedule 10 or Schedule 20 pipes. The thickness varies depending on the pipe size and material.

Schedule 40 steel pipes are often used in applications where high pressure or structural strength is required. They are commonly used in plumbing, water distribution, and some industrial applications.

304 Stainless Steel:

304 stainless steel is a specific grade of stainless steel. The "304" refers to its composition, which typically contains 18% chromium and 8% nickel. It is known for its corrosion resistance and is one of the most commonly used stainless steel grades.

304 stainless steel pipes are pipes made from this specific stainless steel grade. They are resistant to corrosion, making them suitable for a wide range of applications, including food processing, chemical processing, plumbing, and more.

So, when you mention "Schedule 40 pipe 304," you are likely referring to a pipe made from 304 stainless steel with a Schedule 40 wall thickness. This combination offers the benefits of both the corrosion resistance of 304 stainless steel and the strength provided by the thicker wall of a Schedule 40 pipe. It is a common choice for applications where both corrosion resistance and structural integrity are important.