1, Defective square tube because the processing is not in place, the appearance will be a lot of glitches, and these burrs will be very simple scratches the pipe surface, so the first identification method came out, there are many scratches on the exterior of the Is the quality of the poor.

2, Defective side tube manufacturers in order toreach a large negative public service will increase the amount of productprocessing when the reduction, and this will result in products of fine and low cross-ribs, so if you find such a situation, then the best side do not buy.

3, So called square tube is because thecross-section of the pipe is square, and poor side of the pipe in this regardis not in place will make the pipe section of the oval-shaped cross-section.

4, Residual side tube is basically not able to reach the standard specifications, so when you buy with a professional ruler about the volume can be briefly resolved.