the present invention there is realized an improved stability in the area of the screw threads preferably the plastic utilized is polypropylene polypropylene has the advantage of low cost and chemical compatability requirements with the enclosed cosmetic product the use of polypropylene for the lip and skirt areas circumvents any tendency toward stress cracking under load and its use is a major advantage over the use of styrenics or acrylics in place of the polypropylene further by virtue of the provision of the interengaging shoulders 28 and 30 fig7 and 9 which are disposed radially underneath the screw threads 23 forces encountered during screwing or unscrewing of a screw cap 22 are countered by the immediately adjacent shoulders 28 30 and the resulting construction also provides the high resistance to stress cracking noted above especially with certain cosmetic solvents and after the plastic adjacent the screw threads has aged an extent another embodiment of the invention is illustrated in fig1 showing a slightly modified double walled jar 60 the construction involving retention of the inner and outer side walls 62 and 64 respectively is essentially as described above the increased strength of the skirt 66 is also retained in the present construction by the invention a weight 68 is fitted into the downwardly extending skirt 70 on the bottom wall 72 and held therein by a bead.