For small repair jobs, go to a drugstore and find Dental Floss made by W.L.Gore. This is similar to the Super high tech "Tenara" PTFE thread (also by W.L.Gore the maker of 'Goretex').
Both are used with a #16 needle on a sewing machine.
For larger jobs (as someone else also posted) go to: sailrite.com; go to their catalogue to match the thread size to the needle size to the fabric weight.
If you cant find the references, most sails on a Santana 27 will need V-69 polyester thread.
