KSKATE, you need to measure that bobbin and get the exact, repeat , exact measurement for the heighth and width and note the number of holes. Probably the diameter of the holes also. Then you can start looking on the internet on sites that sell antique bobbins and you can compare oranges to oranges in looking f or a match.

If your machine was made in Japan (most likely it was) it will take a class 15 bobbin. That looks like what you have there so you are good to go.

If my machines have been running fine on either metal or plastic bobbins, right size of course, for years, is there something I should be aware of that I am not?

Yes it does matter. You don't have a brother machine otherwise you would have been terrible trouble recently. A brother only works with the correct bobbin.

The way it was explained to me is, if the case the bobbin goes in is metal, then use a metal bobbin. If it is a drop in bobbin and the area it drops in is plastic, then use a plastic bobbin. Like to like.

I agree! My singer takes a 15J bonnin. the bobbin size 15 fits almost but has a little wiggle room so my stitches are not always good!!!!

Yah..I thought my new Janome would be able to use the bobbins from my old Kenmore (since it was made by Janome anyway) but...NOPE! I have 2 Brother machines that can share bobbins but my Janome will not sew right with either the Kenmore or Brother bobbins even though they look pretty much identical to me. It sounds funny and breaks thread. The Kenmore, oddly enough, seems to do fine with just about any bobbin I put in there except the curvy Singer bobbins - I wonder if it's because it's a front-loader instead of a drop-in like my other machines; or if it's just that it's kind of old and wonky in general so I can't tell the difference, LOL. I seem to have lost the manual for that one so I'm not sure what it SHOULD be using. But, it's my backup to my backup so I'm in no rush or worry to figure it out.

Yes, it is very important that the bobbin is correct. I have an older Bernette and the bobbins look just like my old Singer bobbins, but they won't work in the Bernette. I had a terrible time sewing and finally took it in and found out that I had to buy Bernina bobbins. I always make sure I have the correct bobbin for the sewing machine, I don't like seeing all those loops in the bobbin thread or having threads break over and over. Easier to get the correct bobbins first.

I was surprised that several of my sewing machine manuals do not list the bobbin size at all. In fact only my old Singer manuals do.

I know!! It seems like such a basic, BASIC piece of information. I've gone through and handwritten the proper bobbin sizes into my manuals so I won't have to hunt through the internet again next time I need more.