I found that even with Janomes the plastic bobbins are not necessarily interchangeable. I use what is recommended for the machine.

that is true. Some Janome's use the L and some the A. However, my Janome dealer told me that even tho my machines use the A - I can actually use the L but not to refill them. Don't normally do it but it can be done. However, if you have an L bobbin you can't go the other way around because it is a shorter bobbin.

I always use what comes with the machines. I have 2 older kenmores that state in there manuals ( For best stitching results use clear plastic lightweight bobbins when stitching at high speed with widest and longest stitch setting.) To this day I just use the metal ones that also came with them because I am piecing and free motion quilting and don't need the stitch set at the longest stitch setting length. They give me a very good straight stitch. Bobbins are very important in getting good stitch quality.

Suzy

A plastic bobbin came with my machine that is a Brother cs 6000i But I have used the metal ones with no problems. Was always told they were better.

The most important thing is to use the bobbin specified by the owners manual for your particular machine. Just because they actually fit in the case, it doesn't mean you can use that bobbin. it has to be the RIGHT bobbin. It has to have the correct clearance, enough depth so the thread somes out properly - those type of things. Machines take one type of bobbin, and they are not interchangeable.

Yes each machine has a preference. Overall th metal tend to run smoothr especiall in an older machne. I use plastic on my Pfaff 1475 which smy personal machine. However, almost all the vintage machies we have worked n do better with metal. They run smoother, quieter and some hold more thread.
There is a huge variety of bobbins out ther- we still have some w have not been able to identify.

When I took my Janome in for its check up, I got the metal bobbin back in a plastic bag with a note, Use only plastic bobbins.

I have found that most of the books that come with your machines today do specify the bobbin type/class needed. And also read the package when buying bobbins - they list the machine types that particular size bobbin is used in. Some of the plastic bobbins are crowned ( a slight hump) in the center and some are prefectly flat. So, do read carefully.

My flat metal ones do work in my machine that takes flat plastic bobbins.

I use plastic bobbins because that is what came with my Singer Genie back in 1977. Whenever I've had a problem it hasn't been because of the bobbin itself.

Some of the Pfaff will use a plastic bobbin some will not. My 1985 1222 needs a metal one because the bobbin refill is magnetic and you cannot fill a plastic bobbin with it. I tried! My 2004 Pfaff used either metal or plastic. Best to use what is need for your machine. My Janome and Brother bobbins are interchangeable, thank goodness.