an article of thermoplastic material adapted for being molded into a container comprising a tubular neck portion including annular protuberances of hollow ring - shaped profile , and a tubular shoulder portion continuing from the neck portion . the material of the wall of the neck portion is substantially monoaxially oriented and the annular protuberances are circumferentially expanded from the wall without axial strain of the monoaxially oriented material of the wall whereby the material in the neck portion is of substantially uniform thickness and monoaxially oriented therethroughout including the annular protuberances .