A square tube is a hollow structural section with a square cross-section, used in construction and manufacturing. The dimensions are typically specified in millimeters, indicating the width and height of each side. In the case of the 20mm square tube, each side measures 20mm, offering a robust framework for diverse applications. The “50%” designation usually refers to the tube's wall thickness or the fill ratio when discussing load-bearing capabilities, ensuring that the structure can support the desired weight while retaining efficiency.