Abstract: A mold assembly for press molding plastic material into products under heat and pressure wherein the material is placed on a base mold having at least one or more guide blocks spaced thereabout for accommodation of wedge mold segments each having a surface matched to a portion of the base mold. Each wedge mold segment is arranged to move over an inclined surface of a guide block into compression mated association with material to be molded on the respective portion of the mold base to which it is matched. In operation the wedges are pushed downward by a press and moved laterally over the stationary inclined surfaces of the guide blocks which guide the wedges inwardly in matched pressure relation with the material to be molded on the sides of the base mold. The invention also includes division of the wedge mold segment into an assembly of two parts in which a mold section is backed by an associated wedge member which pushes the mold section into molding position.