Hot-rolled silicon spring steel 55Si7 to IS 3431:1982 as amended (Amendments 1 to 3), supplied as bars (also centreless ground or precision bars) and flats for volute, helical and laminated springs for automotive suspension. It through-hardens to at least 54 HRC in oil up to 20 mm round or 16 mm flat, and in the quenched and tempered condition reaches 1320 to 1570 MPa tensile strength. The standard was reaffirmed in 1997 and 2001.