Abstract: A core mold that has a mounting hole on its molding surface and a changeable indicia forming section that is used to form markings on an external surface of injection molded products. The indicia forming section is located on one end of a changeable indicia forming insert. The insert is detachably inserted into the mounting hole of the core mold. A step is also used to prevent the changeable indicia forming insert from moving relative to the core mold. The changeable indicia forming insert is detachably inserted to the core mold so that the indicia forming section is easily changeable by changing the insert. This avoids the delays caused by using core molds and inserts bearing indicia forming sections that are integrally formed from a unitary piece of material. Additionally, the information conveyed by the markings is greater than that possible using core molds with rotary cores.