This part of ISO 630 specifies qualities for seismic-proof improved structural steels. This part of ISO 630 applies to steel plates with thicknesses of 6 mm or over and up to 125 mm, wide flats and hot-rolled sections up to 140 mm, which are used in the usual delivery conditions as given in 6.2 and normally intended for welded or bolted structures. This part of ISO 630 does not include the following structural steels, certain of which are covered by other International Standards: — sheet and strip – refer to ISO TC 17/SC 12, Continuous mill flat rolled products; — tubular products – refer to ISO TC 5/SC 1, Steel tubes.