The utility model provides a core shaft which comprises an injection molding layer, a flat wire layer and a main core, wherein the core shaft is cylindrical; the outer layer of the main core serves as the flat wire layer; the outer layer of the flat wire serves as the injection molding layer; an edge is formed on the outer side of the injection molding layer. As the edge and a protection pipe are in line contact, the contact area between the core shaft and the protection pipe is reduced; friction between the core shaft and the protection pipe is reduced and the sensibility and the use effect of the core shaft are improved.