Industrial Tube & Steel Corporation stocks carbon steel square tubing in A513 (mechanical) and A500 (structural) grades, in a range of sizes and wall thicknesses. A500 structural carbon square tube is used in construction, buildings, towers, and sign support applications, but also in trailers and structural fabrications. A513 mechanical carbon steel square tube is frequently used in the automotive, solar, appliance, and agriculture industries, as well as in many other types of machinery ranging from bases to supports. All ODs below 2" with wall thickness less than .120 inch are typically manufactured as ASTM A-513. Sizes 2" and above with wall thickness of .120 inch and heavier are typically manufactured to ASTM A-500.