The square tube's general length is 4m to 12m, mostly 6m and 12m.

Square tube classification:

1. Section/section shape: square tube (square tube), rectangular square tube (rectangular tube);

2. Surface treatment process: black square tube, hot-dip galvanized square tube, galvanized strip square tube, oil-coated square tube;

3. According to the material: plain carbon steel square tube, low alloy square tube;

4. According to the standard: national standard, Japanese standard, British system, American standard, European standard, non-standard;

5. Production process: welded square tube (longitudinally welded tube), seamless square tube (no weld, changed to drawn tube);

6. Uses: square tubes for steel structures, square tubes for steel beams and columns, square tubes for bridges, square tubes for automobiles, square tubes for machinery industry, square tubes for machine tools, square tubes for decoration, Special purpose square tubes.

The core judgment standard on the national standard:

1. Concave-convexity of the cross-section: no more than 0.6% of the length of the side, the minimum value is 0.4mm (measured at a distance of not less than 100mm from the end);

2. Length deviation: ordinary grade 4m to 12m, allowable deviation 0-70mm; precision grade 4m to 6m, allowable deviation 0-5mm, 6m to 12m, allowable deviation 0-10mm; short length and non-cut length joint pipe weight should not exceed 5% of the cargo volume, and no more than 10% if it exceeds 20kg/m.

3. Surface curvature: not more than 2mm per meter, and the total curvature is not greater than 0.2% of the total length;

4. Weight deviation: actual weight and adjusted weight deviation range -6% to 10%.