If you are really into quilting on your mid arm, consider going all the way with a winder from SWF embroidery machines. It's definately more pricey about $210 as I recall, but I've used mine for 5 1/2 years with no complaints. It has a timer that you adjust. You can put the bobbin on and walk away. Adjust the timer for the thread your are working with - darker colors lower the time a hair and so on. The winder from Kings men works just fine and that's what I started with years ago, but instead of shutting off, the bobbin winder kicks off and the motor keeps racing. Drove me nuts, wasted electricity. I use enough as it is. I'm not sure about the size business. My bobbins are M, but you can ask them.