To design a welded steel stand capable of supporting 600 pounds using 4x4 square tubes, it's essential to calculate the appropriate thickness of the steel tube. The thickness affects the section modulus, influencing stress and deflection limits. A suggested thickness of 3mm is deemed sufficient, considering a plate of 10mm thickness placed over the tube to distribute the weight. Additional details such as the distance between the tubes (397 mm center to center) and the use of galvanized steel with a yield strength of 200 GPa are crucial for accurate calculations. Proper calculations ensure the structure's safety and stability under load.