Square and rectangular cold-formed hollow sections, also known as square tubes and rectangular tubes, with codes F and J respectively.

1. Permitted tolerance for the wall thickness of rectangular tubes: when the wall thickness is not greater than 10mm, it should not exceed ±10% of the nominal wall thickness. For wall thicknesses over 10mm, the tolerance is ±8% of the wall thickness, excluding the bend and weld areas.

2. Standard delivery lengths for square tubes are typically 4000mm to 12000mm, with 6000mm and 12000mm being the most common. Square tubes can be delivered in short lengths of not less than 2000mm or in non-standard lengths, and can also be supplied as joint tubes, but the customer must cut off the joint tubes upon use. The weight of short lengths and non-standard products should not exceed 5% of the total delivery quantity, and for square tubes with a theoretical weight greater than 20kg/m, it should not exceed 10% of the total delivery quantity.

3. The bend of the square tube should not exceed 2mm per meter, and the total bend should not exceed 0.2% of the total length.