Cov hniav conical feem ntau yog siv los ua cov hniav hauv nruab nrab ntawm ib qho kev xyaum me ntsis, haum rau cov pob zeb uas muaj qhov nruab nrab corrosion thiab hardness!Thaum lub pob zeb tseem mos, cov hniav tuaj yeem ua tau!
