[srt9969]

Thanks for the welcome.

Tube can't be stamped before insertion, as the ends are flared to rivet the bead on to the tube. The outside of the tube lies flush against the glass, the inside of the ends forms the flare, and is hammered to shape, which would damage any engraving or etching done prior to insertion. In x-section, the bead looks like this:-
o)(o (well, roughly...)

Thanks for your help,

Regards,

Sean

PS How does etching work? I use ammonium bifluoride to etch glass - is it a similar process?