... ,polished,black Certificate:ISO,SGS Origin:China spring steel features:1, spring steel Size : all size is available.Base on ... : 55 mm--58 mm 2 spring steel Application: used for mattresses 3,spring steel Characteristic: 100% one wire splice free ... structure, with even weight bearing and rational structure, without splice, without breaks or caving in, but with integral type,heat high quality spring steel ...