I have two old Singer machines, almost exactly alike. The one I am presently using, up north, was giving me trouble, the thread constantly breaking, when I would change color I found that it was working fine, this continued back and forth until I realized that when the thread was breaking it was because the bobbin was not wound properly. It took me days to figure that out. I use metal and have at least three different type of plastics and they all work in both my machines (from the '60s) if properly wound. Just something to check. I purchased a set of 6 prewound bobbins and cannot get the thread loose on any of them to be able to use them.

If you have a sewing machine repair shop, go to them with model etc of machine. They probably have older bobbins that will work.
I have a drawer full of old bobbins that have accummulated over the years.

Well I bought another used machine, and guess what its a singer, lets hope it can use some of my bobbins. Its a mid arm on a frame! I'm getting scared about using it.

I too have purchased new bobbins and noticed that they will not work. My DH notice that when he rolled the bobbins they would roll uneven; a sign that they aren't made correctly. I went to a local sewing machine store and purchased a package of 6; only one didn't work. You may want to try a local store, but best is to hunt for original bobbins.

I would ask my local repair shop. They will be glad to help, and probably will give you the advice for nothing

I recently got my machine back from the repair guy that comes in to Joann's to fix machines. He accidently left a bobbin in my machine. It is thicker than the cheap bobbins and holds more thread and has about 8 holes around both sides of the bobbin. I had the same problem you have with bobbins until I used his bobbin. My thread does not jump out of the bobbin case with this new bobbin. I'm on the hunt for this new found bobbin the repair guy left in my machine.

That machine uses the Class 66 bobbins and if you go to Walmart get the Singer brand metal bobbins 4/.97 and they work!! I have a 66 that is finicky as they come and these are the only bobbins other than the ones that came with the machine in 1921 that it will use. I have miked them out and they are verbatim to the ones made then.

I normally stock these bobbins in my shop and I have never had any complaints.

Billy

Unfortunately, I think a lot of the stuff is made in the same place these days. Probably wont get any better or cheaper until we all stop buying it and they have to think of a better way to corner the market.

I finally asked at a local thrift store why I never see any sewing machine attachments, bobbins, etc.---she said "we throw them out ". figured no one could use them !they must still do it because I rarely see bobbins.

I have an old Singer and have gotten bobbins and other items for it from the Sewing Shop in Arizona. They have a wide-range of Singer items and service and prices are excellent. They can be reached at: http://www.sewingshop.com/