A mold member has a cavity defined by a wall having a groove therein opening into the cavity and within which is accommodated a flexible bar having a smooth edge confronting the cavity. The opposite edge of the bar is slotted at intervals along its length so as to render the bar flexible in its own plane. Rotary adjusting cams are accommodated in openings formed in the bar between adjacent slots for effecting adjustments of selected portions of the bar into and out of the cavity, thereby to enable the effective wall thickness of a molded product to be varied.
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