Thanks Jon, that is interesting to know. I've got two Standard rotaries, and we already figured out that the class 15 bobbin will work in the rotary machines, so it looks like the 15x1 needle will work too. BTW - anyone reading, though it's a "class 15" bobbin and a 15x1 needle, the numbers aren't related - Almost all Singer machines take the 15x1 needle, and Singer's number is 2020 for it. Most vintage Singers don't use the class 15 bobbin either.