I started out using the jewelers twine Jeff sells it worked ok but I had a lot of thread snapping, Then I tried the sinew, I thought this broke easier than the jewelers twine. I finished my first Kayak with the jewelers twine doubled and it was better, but I still had some snapping. On my second Kayak tried the mason's twine and even though it appears heavier, I was still snapping as easy as the the jewelers thread when tugging the fabric tight. Then I tried some 65 lb spiderwire braided fish line, and decided it is the the way to go. I had zero breaks and found I was drawing the fabric really really tight. This stuff is thin and strong I use it doubled. over. This stuff is so strong I noticed that my gunwales were slightly bowed in between the frames because of pulling the double corded method. (It made for a nice tight finish)
attached is a picture of ny cheapskate's thimble, It works really really well. (A 12 ga. shotshell hull cut down)