A question I get asked fairly frequently is where to find single-strand thread for making tapered waxed ends for sewing.
It’s hard to get really good stuff these days because there isn’t really anywhere doing proper long-staple linen anymore but you can still get workable stuff.
The stuff you want is ‘number 10 shoe thread’. It is dry spun single-ply linen. Dry spun is important, because wet spun doesn’t take wax nearly as well.
I haven’t used any of these suppliers, I bought 250 balls of vintage 1940s thread from an ebay seller a few years ago so I don’t really need any more.
Another place to get it is here:
If you come across any other suppliers, please leave a comment and I’ll add them to the list.
Another thing you can do is use polyester/dacron thread. That might seem heretical for medieval work but it’s functionally identical to linen, easier to source, and will never rot out and it’s better to be making stuff with imperfect materials than not making stuff at all.
You can get pre-tapered lengths for hand sewing but they’re all pre-waxed with parrafin wax, which is completely the wrong stuff. You can soak that off in kerosene though and re-wax them with code to get nice locked up stitches.
DW Frommer, a bootmaker who I admire greatly has a photo essay on tapering dacron thread on the Crispin Colloquy. The same process works with linen.