@ vintagerose: Thank you for the suggestion. I tried, but at diameter 32mm it is a bit large so standard candles flop over. If it is, it is not for present day standard candles.
@ Anne: Good thinking, it contains around 2,5 ml so it might be a posh bar measure! I don' think it is a stopper though - I cannot see the rounded shoulders sit in the neck of a decanter.