I used to use polyester sailthread for my bags - https://shop.solentsew.co.uk/thread/bonded-polyester.html (nylon soaks up water and then stretches much more than polyester)
Depending on the machine you might get away with V92. V69 should be fine for domestic machines generally. https://www.sailrite.com/Selecting-the-Right-Thread-Size#:~:text=V%2D69%20is%20the%20heaviest,of%20thread%20on%20the%20spool.
@danb started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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I used to use polyester sailthread for my bags - https://shop.solentsew.co.uk/thread/bonded-polyester.html (nylon soaks up water and then stretches much more than polyester)
Depending on the machine you might get away with V92. V69 should be fine for domestic machines generally. https://www.sailrite.com/Selecting-the-Right-Thread-Size#:~:text=V%2D69%20is%20the%20heaviest,of%20thread%20on%20the%20spool.