|This is probably obvious to many people, but I only just figured it out this winter.
I like to buy large spools of thread for economical reasons, but I also like to topstitch with double needles. Instead of buying two large spools, I buy just one and then wind a bobbin for the second needle.
Sometimes my thread spools are too big to fit conveniently on my machine, too. In that case, I wind two bobbins and use them both as if they were small spools.