Bobbin Keeps Jamming? Six Causes and How to Fix Each

A jam that happens repeatedly, not once, almost always comes down to one of six things: insertion direction, an unevenly wound bobbin, the wrong bobbin class, lint, a damaged bobbin edge, or a loose screw in the bobbin case. Work through them in order.

An occasional jam can be a fluke. A bobbin that jams every few stitches, or jams the same way every time you sew, has a specific cause. Here's the order to check them in, starting with the fastest to rule out.

1. Insertion direction

The bobbin has to unwind in a specific direction once it's in the case. If it's in backward, thread can catch on the case's edge and jam within the first few stitches. Remove it, flip it, and reinsert following the direction diagram usually printed on or near the bobbin case.

2. Unevenly wound bobbin

A bobbin wound with thread piled unevenly to one side (thick on one edge, thin on the other) feeds inconsistently and can catch on the case as it unwinds. If you can see uneven winding by eye, rewind it rather than trying to sew through it. See our guide on winding a bobbin evenly for the routine that prevents this.

3. Wrong bobbin class for your machine

A bobbin that's close to the right size but not an exact match for your machine's bobbin class can sit slightly loose or slightly tight in the case, which shows up as intermittent jamming rather than a bobbin that won't fit at all. Check your machine's manual for the exact class it calls for, whether that's Class 15, Class 66, or a brand-specific class like SA156.

4. Lint in the bobbin case

Lint collects in the bobbin case and around the hook mechanism from ordinary use, and enough of it changes how freely the bobbin turns. Brush the case and the surrounding area out with a small brush after every few bobbins, more often if you sew a lot of quilting cotton or fleece.

5. A damaged or nicked bobbin

A small nick or burr on the edge of a bobbin, plastic or metal, can catch thread every time it passes that spot. If a specific bobbin jams no matter what you do, and a different bobbin in the same machine doesn't, retire that bobbin rather than continuing to sew with it.

6. A loose bobbin case screw

On machines with a removable bobbin case, the small screw that holds the tension spring in place can work loose over time. A loose spring changes how the case grips the bobbin and can cause repeated jamming that looks like a bobbin problem. This one is worth a technician's eye if the first five checks don't resolve it.

Still jamming after all six?

If you've worked through all six and it's still happening, the cause is likely in the machine's timing or hook mechanism rather than the bobbin itself, and that's a repair shop job, not a DIY one. But most repeated jams trace back to one of the six causes above.