Thread breaks for four reasons, and only one of them is tension.
A rough spot somewhere on the thread path. Run the thread slowly through by hand and feel for a catch. Burrs form on the needle plate around the hole, on the bobbin case, and occasionally on a thread guide. A burr on the needle plate is common on machines that have hit a pin.
A blunt or wrong needle. A blunt tip needs more force to enter, which shocks the thread on every stitch. Change it — it costs under a euro and it is the fastest thing to rule out.
Thread too heavy for the eye. If you are using topstitch or upholstery thread through a universal needle, it shreds against the eye. Use a topstitch needle, which has a larger eye and a deeper groove.
Tension genuinely too tight. Only consider this after the first three. Reduce the top tension a half-number at a time.
One more, easily missed: cheap thread. Bargain thread has weak spots along its length and sheds lint that packs into the tension discs. If the breaks are random rather than at a particular point in the stitch cycle, and everything else checks out, change the thread before you change anything mechanical.
Questions people actually ask
It breaks at the same point every time.
That points to a burr or a mechanical catch. Turn the handwheel slowly by hand and watch where the thread snags — it will usually be visible.
It only breaks at speed.
Usually the needle eye or the thread quality. At speed the thread passes through the eye far more times per second, and a marginal pairing fails.
Last reviewed 2026-08-11