Yog hais tias koj yuav ib tug tsiaj aub tawb, koj yuav pom tias tus tsiaj aub tawb muaj steel hlau los yog square tube ncig raj aub tawb. Rau cov dev me, steel hlau tuaj yeem siv tau, tab sis rau cov dev loj thiab muaj zog dua, koj yuav tsum xaiv lub raj square raj, uas muaj zog ntau dua li cov hlau hlau. Qhov zoo ntawm cov hlau hlau yog tias koj tsis xav tau nws lawm, nws tuaj yeem muab tais thiab muab tso tseg.
