Raws li qhov sib txawv ntawm qhov hluav taws kub ntawm steel qhov rooj, lawv qhov hluav taws kub kuj tuaj yeem muab faib ua peb qib: A, B thiab C. Steel qhov rooj hluav taws ntawm cov qib sib txawv tuaj yeem siv rau ntau qhov chaw. Qhov zoo ntawm cov qhov rooj hluav taws steel ua rau lawv tuav lub lag luam loj hauv cov tsev pej xeem.