Abstract: In apparatus for molding glass bottles having externally threaded necks, neck ring mold halves are given greatly increased life between down time, as well as increased ease of service, by machining away the threaded cavity portion below the well which accommodates the guide ring, so as to provide a somewhat rectangular recess in the bottom portion of each mold half, and inserting and securing in each mold half a sintered metal threaded cavity insert. Where a double lead thread is utilized, the inserts may be identical in each mold half. Great precision is afforded to the inserts when formed oversize by pressing in a direction perpendicular to with the parting plane, the oversized outer edge surface being then machined parallel to the parting plane to fit precisely within the recess.