Mold base is a comprehensive name used for the parts for containing the cavity for plastic injection mold, and also has the role of directly installing the mold to the plastic injection molding machine.

Mold base is a set of parts that constitute the outer periphery part of a plastic injection mold, and is constituted mainly from the following parts.

Although previously the constituent parts of a mold base were all designed and manufactured as required, standard mold bases have recently come into wider use and are being used all over the world. In the case of large sized molds or small sized molds, even at present, they are being designed individually for each mold.

Although the standards for mold bases have been prepared in Japan in metric units, they are still being prepared in inch units in the U.S.A. In Europe, as in Japan, it is common to prepare them in metric units.

The following two types of structures are the most commonly used ones for the structure of a mold base.

The selection between these two structures is determined by the method of the gate used. When adopting a pin point gate structure, always the structure (2) is used. In the case of a side gate or a tunnel gate, the structure (1) is used normally.

The material for the constituent parts of the mold base is generally the carbon steel for machine construction (S55C, 220C, etc.,) and is used most often in the non-hardened condition. In special applications, pre-hardened steel, or stainless steel, or an aluminum alloy is used some times. A mold based used in combination with accessory parts like guide pins, guide bushes, return pins, etc.