The smallest BSP thread is 1/16" with an OD of over 7mm, so it might not be in that series.
There is a picture of spare parts for one model of can here:
https://www.ajreeves.com/12461.html
Please confirm it is the part bottom left of the picture.
Have you any known bolts that you can use as a thread gauge to judge the pitch? How have you determined it is coarser than 0.75mm pitch? What is the actual OD of the thread?
Cut the end off the delivery tube at the bottom of the internal threads and thread it a known, suitable internal thread (you are extending it, so just extend it 10mm more). Turn down the nozzle, soft solder on a plain sleeve and apply male threads to match the new internal ones.