Square steel tubes are available in sizes that range from 0.5 inches square to 16 inches square, and the internal wall dimensions can range from 0.065 inches thick to 0.625 inches thick. The length of square steel tubes generally ranges from 12 inches to 20 feet.
Smaller square tubing sizes increase in increments of about 1/4 inch. Common sizes are 0.5, 0.625, 0.75, 1.00 and 1.25 inches square. Square tubing larger than 1.25 inches square generally increases in 1/2-inch to 1-inch increments, up to 16 inches square.
Some common internal wall dimensions for steel tubing that is less than 4 inches square are 0.065, 0.083, 0.109 and 0.120 inches thick. Common wall dimensions for steel tubing that is larger than 4 inches square are 0.188, 0.250, 0.312, 0.375, 0.500 and 0.625 inches thick.
American Society for Testing and Materials A500 and A513 mild steel, in grades A, B and C, are used to make hot roll square steel tubing. An increase in alphabet letters indicates an increase in the tensile strength or yield strength of a steel product. ASTM A847 high-strength, low-alloy structural tubing offers improved atmospheric corrosion resistance, and it is used for both cold-form welding and seamless structural tubing.