All bobbins are not equal
How many of us have had boxes of bits that have been passed on from friends and family? Do the boxes include an assortment of bobbins? They often do. I’m sorry to disappoint you but it is unlikely that you can use the different bobbins in your machine. You see, all bobbins are not equal.
As well as some being metal and some being plastic, they come in different shapes and sizes. The differences are often very subtle, a few mm different in height, a slight dome shape to the sides, you often can’t tell unless you look very closely and even then, it may not be obvious. For example, I have a Brother machine which I use at home and the Janome machines I use for teaching. They both have plastic bobbins that look very similar but they are not the same and cause problems if the wrong one is used. I have to be very careful about keeping them separate. Thankfully, there is a difference I can see but only in daylight! There is a very slight blue tint on the brother bobbins and a very slight yellow tint on the Janome bobbins so I can tell the difference. So, if you are having problems with your machine and you have checked that it is threaded properly, the needle is new, the tension is right and anything else you can think of, make sure the bobbin you are using is the right bobbin for your machine. You can browse various bobbins here and if you are not sure whether the bobbin is right, call into Jaycotts with the make and model of your machine, they may well be able to supply you with the right bobbins.