Abstract: Present invention relates to a metal mold device comprising a female die, a die frame having a hole and a male die assembly moving along an axis of the hole to produce a plastic molding having an opening with a partially waved inner sidewall. The male die assembly comprises a generally upwardly tapering central base having a rectangular top and four side slopes, a pair of opposed primary slide members and a pair of opposed auxiliary slide members. The primary slide members are strictly mounted on the opposed side slopes respectively while the auxiliary slide members are loosely mounted on the remained opposed side slopes respectively.