IEC 60329:1971

Limited to strip-wound cut cores, in both single-phase and three-phase forms of construction, having rectangular cross-sections and rectangular windows (coil spaces), manufactured from cold-reduced grain-oriented silicon-iron alloy strip, and for use in transformers and inductors for telecommunication equipment and for electronic devices.
May be generally applied to cores of other than rectangular windows or cross-sections. In this case, certain characteristics, e.g. electrical properties and dimensional tolerances shall be the subject of special agreement between user and manufacturer.