Brother machines use one of two bobbin sizes, and the wrong one will jam or skip stitches
Most Brother sewing machines take either a Class 15 bobbin (the smaller, plastic kind) or a Class A bobbin (the larger metal kind). Which one your machine needs depends on the model. Class 15 bobbins are about the size of a dime and fit machines like the Brother CS6000i, the XM2701, and most entry-level models. Class A bobbins are noticeably larger—roughly the size of a quarter—and fit heavier-duty machines like the Brother PQ1500S and some commercial models.
The easiest way to know which bobbin your machine takes is to open the bobbin case and look at what's already in there. If you've lost the original bobbin or it's too worn to identify, check the manual that came with your machine—it will list the bobbin type in the specifications section. You can also find your model number on the back or bottom of the machine, then search "[model number] bobbin size" online, or call Brother customer service with the model number and they will tell you when ready.
Using the wrong bobbin size will cause visible problems: the thread will either wind too loosely (and create loops on the underside of your fabric) or won't fit in the case at all. Never force a bobbin into the case if it doesn't slide in smoothly—you risk damaging the bobbin case itself, which is expensive to replace.
Key Takeaways
- Brother machines use either Class 15 (small plastic) or Class A (large metal) bobbins, and your machine manual or model number will tell you which one.
- The bobbin already in your machine is the correct size—if you need a replacement, match it exactly.
- Class 15 bobbins fit most home sewing machines; Class A bobbins fit heavier machines and some commercial models.
- Using the wrong bobbin size causes thread tension problems and can damage the bobbin case if forced.
- Brother bobbins are inexpensive and widely available at fabric stores, online retailers, and directly from Brother.
How to identify your machine's bobbin type without the manual
If you don't have the manual, the fastest method is to remove the bobbin case and measure what's inside. Open the needle plate (the metal cover under the presser foot) and look at the bobbin case—the small metal or plastic housing that holds the bobbin. If the case is about the size of a postage stamp and holds a bobbin the size of a dime, you have a Class 15 machine. If the case is noticeably larger and the bobbin is closer to a quarter in size, you have a Class A machine.
Another reliable way is to look at the bobbin case itself for printed text. Many Brother bobbin cases have "Class 15" or "Class A" printed directly on them. If you can't see text on the case, take a photo of your machine's model number (found on a sticker on the back or underside) and search for it on the Brother website. The product page will list the bobbin type in the specifications or accessories section.
If you're at a fabric store or online retailer and unsure, you can also buy a small pack of each type—they're inexpensive—and test which one fits smoothly into your bobbin case. The correct bobbin will slide in and out without resistance. Do not force either one; if it doesn't fit easily, it's the wrong size.
Class 15 bobbins and which Brother machines use them
Class 15 bobbins are the standard for most Brother home sewing machines. They are small plastic spools that hold a moderate amount of thread and work well for everyday sewing on light to medium fabrics. Common Brother models that use Class 15 bobbins include the CS6000i, XM2701, LX3817, HC1850, and most machines in the Innov-ís and Designio lines.
Class 15 bobbins come in two styles: plastic bobbins with a metal center (the most common) and plastic bobbins with a plastic center. Both work in the same machines, so either style is fine. You can buy them individually or in packs of 10 or more. Brother brand bobbins cost a few dollars per pack, and generic bobbins made by other manufacturers (like Coats or Gutermann) are often cheaper and work just as well.
One thing to know about Class 15 bobbins: they wind more slowly than Class A bobbins because they hold less thread. If you do a lot of sewing, you may need to rewind bobbins more often. This is normal and not a sign of a problem with your machine.
Class A bobbins and which Brother machines use them
Class A bobbins are larger and made of metal, and they hold significantly more thread than Class 15 bobbins. Brother uses them in heavier-duty machines designed for thick fabrics, quilting, or extended sewing sessions. Models that typically use Class A bobbins include the Brother PQ1500S (a quilting machine), some industrial-style models, and certain commercial machines.
Class A bobbins are less common in home sewing than Class 15 bobbins, so they can be harder to find in regular fabric stores. You may need to order them online from Brother directly, from quilting supply shops, or from industrial sewing retailers. They are more durable than plastic bobbins and last longer, which makes them worth the extra cost if you own a machine that uses them.
If you own a Brother quilting or heavy-duty machine and are unsure whether it uses Class A bobbins, check the manual or contact Brother support. Using a Class 15 bobbin in a Class A machine will cause the bobbin to fall out of the case, and using a Class A bobbin in a Class 15 machine will not fit at all.
Where to buy Brother bobbins and what to expect to pay
Brother bobbins are sold at most fabric stores (Joann, local quilt shops), online retailers (Amazon, Etsy, eBay), and directly from the Brother website. A single bobbin costs roughly 50 cents to $1.50, depending on whether you buy them individually or in bulk. A pack of 10 Class 15 bobbins typically costs $5 to $8. Class A bobbins are more expensive—usually $1 to $2 each—because they are metal and less commonly needed.
Generic bobbins made by other thread manufacturers work fine in Brother machines and are often cheaper than Brother-branded bobbins. The important thing is matching the size (Class 15 or Class A), not the brand. If you buy online, make sure the listing clearly states which class the bobbin is, because a mislabeled product will not fit your machine.
If you cannot find the exact bobbin type locally, ordering online usually takes 3 to 7 days. In the meantime, you can rewind an existing bobbin if you have one, or ask a local fabric store if they have a loaner bobbin you can use while you wait for your order to arrive.
How to wind a bobbin correctly so it doesn't cause tension problems
If you have a bobbin but no thread on it, you can wind it yourself using your machine's bobbin winder. Most Brother machines have a bobbin winder built into the top or side of the machine. To wind a bobbin, place an empty bobbin on the winder spindle, thread the machine as if you were sewing (but without a needle), and press the foot pedal or press the start button. The machine will wind thread onto the bobbin automatically.
Wind the bobbin until it is full but not overstuffed. A bobbin that is wound too tightly or too loosely will cause thread tension problems—the stitches on the underside of your fabric will look loose or loopy. The bobbin should feel slightly springy when you press it gently with your finger, not rock-hard. If the winder keeps spinning after the bobbin is full, stop it manually and cut the thread.
Always use the same type and weight of thread for the bobbin as you use in the needle. If you use heavy thread in the bobbin and light thread in the needle (or vice versa), the tension will be unbalanced and your stitches will look uneven. Most home sewers use all-purpose polyester thread in both the needle and bobbin, which works well for most fabrics.
Troubleshooting bobbin problems: when stitches skip or loops appear
If your machine is skipping stitches or creating loops on the underside of your fabric, the bobbin is often the culprit. First, check that you are using the correct bobbin size for your machine. If you recently switched bobbins or bought new ones, make sure they are Class 15 or Class A as appropriate. A bobbin that is even slightly the wrong size will cause these problems.
Next, remove the bobbin and inspect it for damage. Bobbins can crack or develop rough edges if they fall on a hard floor or if thread gets caught in the case. A damaged bobbin will snag the thread and cause skipped stitches. If the bobbin looks cracked or dented, replace it with a new one. If the bobbin looks fine, remove it and rewind it—sometimes a bobbin that was wound unevenly or too tightly will cause tension problems.
If you have tried a new bobbin and the problem persists, the issue may be with the bobbin case itself (it may be bent or dirty) or with the needle. Clean the bobbin case with a small brush to remove lint and thread bits, and replace the needle with a fresh one. If problems continue after that, contact Brother support or take the machine to a repair shop, because the issue is likely inside the machine.
Frequently Asked Questions
Can I use a Class A bobbin in a Class 15 machine?
No. A Class A bobbin is too large and will not fit in the bobbin case of a Class 15 machine. Forcing it in will damage the case. Always use the bobbin size your machine is designed for.
Do I need to buy bobbins from Brother, or will generic ones work?
Generic bobbins work fine as long as they are the correct size (Class 15 or Class A). Brother-branded bobbins and bobbins from other thread companies like Coats or Gutermann are all compatible. Generic bobbins are often cheaper and perform just as well.
How many bobbins should I have on hand?
Most sewers keep 5 to 10 wound bobbins ready so they don't have to stop and wind a new one mid-project. If you sew frequently or use many different thread colors, having more bobbins is convenient. If you sew occasionally, 3 to 5 is usually enough.
What happens if I use the wrong bobbin size?
The wrong bobbin will either not fit in the case at all, or it will fit loosely and cause thread tension problems. You may see loops on the underside of your fabric or skipped stitches. Never force a bobbin into the case; if it doesn't slide in smoothly, it is the wrong size.
Can I wind a bobbin by hand if my machine's winder is broken?
Yes, but it is tedious and the result is usually uneven. You can wind thread onto a bobbin by hand using a pencil or dowel through the center hole to spin it, but the tension will be inconsistent. It is better to have the winder repaired or to buy pre-wound bobbins until the machine is fixed.