Rolling Shutter Spring Steel: 1) Width: 20 - 250mm 2) Thickness: 0.10 - 2.5mm 3) Material: 50#, 65Mn,60Si2Mn, T8A, T10A Rolling Shutter Spring Steel:1) Color: deep blue polish, grey blue2) Used for rolling shtter spring door3) Superior in flatness, stability, useful material coefficient and surface smoothness4) Various steel grades: (1.0-2.0) x (40-80) mm5) Material: ck67, ck 72, ck 75