Abstract: Method for processing glass coated tubular metal inserts for use in forming apertures employed in the manufacture of all-glass multiple sheet glazing units. The surface of the metal inserts are first cleaned and then their outer surfaces are prepared to receive a layer of glass frit by tumbling in sand. The layer of glass frit is physically adhered to the clean outer surface by tumbling the inserts in small pieces of glass. The glass fritted inserts are then treated in a continuous operation, at elevated temperatures by first degassing the glass frit layers in a vacuum, oxidizing the outer surface of the metal inserts at a temperature below the sintering temperature of the glass frit in a controlled atmosphere, and then sintering and glazing the glass frit layer at a temperature above the softening point thereof while still in a controlled atmosphere to securely bond the glass layer to the metal inserts.