This is a bobbin case for a 5.5 mm machine. It has what is called a "stitch finger" on the case. This type of bobbin case is for machines with a hook system that is called a "CB Hook." It is advantageous to thread your 'stitch finger' whenever you want to stitch a satin stitch, or any satin-type, heavier, decorative stitch. Why? VIP TIP: Threading your thread through the stitch finger puts MORE tension on the bobbin thread, which is what you WANT when you are stitching decorative stitches OR a compact zig zag satin stitch. It will prevent the bobbin thread from coming to the top, which isn't attractive in a decorative stitch.The bobbin case to the left is for machines with a 9mm stitch width. This type of bobbin case is used for 9 mm machines with a 'rotary hook" type of system. The pigtail bobbin case acts like the case above with the stitch finger, only it's for 9mm machines. Also, this 'pigtail' case is required when you are using the embroidery module on your machine. It puts more tension on the bobbin thread when embroidering... which is what you want so the bobbin thread won't come to the top. You may want to try using this case with your decorative stitches on these types of Bernina machines.
It's my personal preference (and recommendation) to purchase a separate bobbin case for bobbin play. That way I never have to adjust the screw to loosen the tension on my bobbin case. You can see the screw in the picture to the right. To loosen a bobbin case, it's "righty-tighty and lefty-loosey." You can see in this picture that the screw is set at a clock position of approximately '10 minutes til.' That is how you begin to determine how much looseness you want in your bobbin case. Sometimes it works to have it at about '13 or 14 min til' - or in other words, at almost quarter til, as you look at the face of a clock.It is SO important that you know about the spring that is inside a rotary hook machine or 9mm machine. If you look at your bobbin case (in Berninas), and it doesn't look aligned like it is in this picture, then an adjustment needs to be made. It's easy to do yourself, but it's best to consult a Bernina dealer for the details. (see last picture for more images of the springs). You don't always need to take your machine into the shop when you know the difference, or if you're not sure, just take the bobbin case in instead of the entire machine. If the spring is missing altogether, then you must get a new spring. It's that essential. It's quite easy for a spring to pop out if you drop your bobbin case! If you can find it, you put it back in with the center of the spring 'popping out' ever-so-slightly. This is only related to 9 mm machines. Note: 5mm machines do NOT have this spring. It is also important that this spring be aligned inside the case properly. Just as it is in this picture is perfect placement. You also want to take your brush and clean out any lint that may be hiding around the perimeter of your bobbin case and/or spring! But... gently! This spring can, (and does) 'pop' out if you brush it too hard.
In the picture below, are three types of bobbin cases:
Far left: 5mm bobbin case with the stitch finger.
Center: standard 9 mm bobbin case
Far right: 9mm case with the pigtail (little curley-q wire thingy at the top of the case) and a gold latch. This case is most typically used for embroidery, but is not limited to just that function!
Now this is what you DO NOT WANT --- a badly wound bobbin! It will definitely cause you lots of problems if you sew with it. I show this bobbin in my classes as an example. It typically happens when the bobbin begins to wind in the beginning. Usually the thread hasn't been adequately secured onto the bobbin core. Some threads, especially rayons or polyesters can be tricky to secure at first, as they tend to slip off before your winder can get a few wraps securely on he bobbin center. You can see the brown thread in the bobbin below it; properly wound, smooth, even and firm. You should never be able to feel that the bobbin thread is 'spongey' or has alot of 'give' to the touch.
You also do NOT want a thick bobbin thread to look like this (see below) in the bobbin! Notice the little metal 'grippies' that help the thread to cling to the bobbin when you first begin winding? If you wrap your thread at least 5-6 times around before you begin the winder, your thread should stay nice and firm as it fills up in the bobbin.
Here is a perfectly wound bobbin. Ahh... now that's nice!
Below: a picture of a 5mm case (note there is no spring), and a 9mm bobbin case WITH a spring. The spring always needs to be aligned properly within the case. If you've ever dropped your bobbin case, and the spring pops out, you can easily put it back in, but there is a right way and a wrong way! Check with your dealer, if you're not sure. The little center circular piece should 'pop' out ever so slightly, and the notches that are on the spring should go into their proper notches that match in the bobbin case.
VIP tip: Always thread your bobbin case with the bobbin turning to the right, clockwise, with the bobbin facing you. And if you suspect something 'isn't quite right' ---check it again!