I use a 14mm tool that fits a 15mm socket, see attached photo, it was the first tool I bought for my Fulvia in 1984, via Snap On or similar supplier.
if it does then I have one too which I bought back in the day in the mid eighties when I had an Hpe. It is now a critical tool in France to do oil changes on my Delta!
Pretty sure this is the tool I use for the Beta sump too. I would have bought it in 1991. I recall the other end worked on the plug of my 205 Gti.
