1. According to the cross-section shape, there are round (wire diameter 5-9mm) and rectangular (16mmx7mm, 12mmx2mm) and so on;
2. According to the type of powder core, there is a single, composite, a variety of single mixed and so on;
3. According to the division of the way out of the line, there are external and internal shaft type;
4. According to the division of forming methods, there are lap type, welding type and bite type;
5. According to the core material state division, there are loose and whole (powder extrusion).
