Actually it's a push in tenon made to look like a military mount and I have a weakness for the military mount.
Many estate 920s from different lines have the vulcanite stems, but Savinelli's modern production is mostly acrylic. I restored a Portofino a few months back for forum member pioesmokingtom, and it had a vulcanite stem.Is it only the Roma line that comes with a vulcanite stem?