A mold for the manufacture of plastic objects has a plurality of cavities which are formed by clamping together a plurality of individual insert straps. The insert straps each have a shape corresponding to a portion of the desired cavity and the insert straps in combination form the desired cavity The insert straps may be rearranged and straps may be added or withdrawn to provide cavities of different lengths and configurations. The mold also has a sub-ejector assembly which may be positioned to accommodate changes in the size of the individual cavities formed by the combination of insert straps The method for making a mold includes the steps of forming a mold cavity using a plurality of insert straps and then clamping the individual insert straps together.

An injection molding mold includes a columnar core mold and a pair of split molds disposed so as to surround the entire periphery of the core mold. The injection molding mold effectively degassing the inside of a cavity for molding an irregular tubular molded article opened at one end and closed at the other end. A piece plate stack (J), configured such that a plurality of degassing piece plates P.sub.1 to P.sub.4 is stacked on each other, is integrally incorporated into a portion of each of a pair of split molds (B.sub.1, B.sub.2) forming a box-shaped second cavity of a cavity, and degassing grooves G.sub.1 to G.sub.4 formed in each of the degassing piece plates P.sub.1 to P.sub.4 are covered with another degassing piece plate P.sub.2 to P.sub.4 located immediately thereabove. Gas accumulated in the cavity is discharged to the outside of the molding mold through degassing holes H.