Thank you VT however not long after this pic was took I ran into a problem, not with the attachment but with my lathe there must be a broken tooth inside the screw cutting gearbox and it started to jump. Luckily I was not leaving it unattended and managed to withdraw the cutter before it did any damage to the part but it would not do another run without jumping so the finished part is not quite as deep as I wanted but it will do the intended job well enough.
If I wanted to make another the next option is 2 1/4 tpi which would still do but I only want one for my quornish project.