... Surface:bright,polished,black Certificate:ISO,SGS Origin:China spring steel features:1, spring steel Size : all size is available.Base on customer’s ... : 55 mm--58 mm 2 spring steel Application: used for mattresses 3,spring steel Characteristic: 100% one wire splice free spring series, this kind of ... , without splice, without breaks or caving in, but with integral type,heat high quality spring steel