I us both on my regular machine they use the older classic model 66.

I use prewound (on cardboard) Bottom Line bobbins in my Janomes - work well

I use both in my Janome, but find it works better with plastic bobbins...don't know why tho'..

One of my students was told by some salesman that she could use a 'universal bobbin' that would work in any machine. Needless to say, that was untrue. She was having all kinds of trouble trying to make a stitch, and as soon as I saw the bobbin in the bobbin case, I could see that it was not high enough. I switched out her bobbin, and it was fine.

Not all bobbins are created equal. Many look very much alike, but are not.

Most classic machines these days take ONE of the following: class 15, 15J, class 66. Class 15 and 66 are available in both plastic and metal. I don't think I have seen any 15J in metal. Singer 221, 222 & 301 all take a class 221 bobbin, and I have only seen these in metal.(There are other bobbin types besides these.)

The rule of thumb is, if your bobbin case/carrier has any plastic in its construction, use plastic bobbins. If it is all metal, you could use either. That said, I have found that some machines perform better with one or the other. If your manual recommends one over the other, I'd stick with that.

all I know is you need the correct size for the machine. I was teaching a class once that a gal was having all kinds of tension problems. Her bobbin was a smig to tall. She had bought some that "LOOKED" the right size. We changed her bobbin and all was well. SO, use the one made for the machine....

I can't use metal bobbins in my machine (Janome 6600)because it's manufactured with a magnet under the bobbin holder somewhere.

ty for your replies. I have a sewing group I attend on Tuesday and their always having trouble with the machines. I tell them to use the correct bobbin that came with our machines, but they say it doesn't make a diff. I will continue to use the bobbins that came with my machine. I have no problem.
Happy quilting,simple quilter

My sewing repair man says "if it came with plastic, do not use metal bobbins", it all has to do with timing, bobbin weight, and other things that I didn't understand, but I do trust him and so only use plastic in my Kenmore. My Pfaff uses metal bobbins. I buy plastic bobbins at Hancock but read the packages that tell me what machines they are for because sometimes they look right, but do not work.
Brenda

I was so stupid I did not "see" that "Singer" bobbins were different heights. After spending a sewing doctor fee to learn that my "problem" was using the wrong height of a Singer bobbin, I would say YES, be careful. I felt so DUMB.

Like your closing. Happy Quilting, simple quilter.