6061 Aluminum Square Tube is an oven-baked, processable alloy. This is done to help increase the overall hardness. The higher the "T" representing the tempered state, the longer the workpiece has been heat treated and therefore the harder the material should be. If something is labeled "T6" it is the hardest tempering option for 6061 alloys. The extruded flat steel complies with 6061-T6511 standard and the plate is a 6061-T651 product. Because there is an additional item at the end of the name, the part must be re-ordered, or the ordered part must be re-machined. 6063 aluminum square tubing is considered one of the lower strength options of the two materials found here. Typically, it is sized for thinner wall designs. It also has better corrosion resistance and a more attractive surface quality than 6061. 6061 is most commonly used in structural applications requiring greater strength and stability. As mentioned above, 6061 aluminum square pipe can be used in a variety of industrial purposes.​These include: Automotive applications such as couplings and valves Structure leisure products machined parts Fixtures.