An apparatus for manufacturing a glass stem for an electron tube comprises a first mold assembly and a second mold assembly for forming the stem therebetween. The glass stem includes a plurality of fillets with a lead-in conductor through less than all of the fillets and at least one dummy fillet without a lead-in conductor therethrough. The first mold assembly includes a universal stem having a mold block with fillet-forming openings therein. A replaceable marker pin is disposed and retained within the openings. The marker pin has a first end and an oppositely disposed second end. The first end has a distinctive geometric shape for contacting the dummy fillet and for conveying intelligible information thereto.