It sounds obvious, but the thread is always worth checking first.

• Make sure you're using thread suited to your project - cotton for cotton fabrics, polyester for most everything else
• Avoid cheap or old thread - low-quality or aged thread is brittle and prone to snapping
• Check you're not using hand sewing thread by mistake - it's often pre-waxed and doesn't behave well in a machine
• Metallic and invisible threads need a specialist needle and slower speeds to behave themselves

A tired or wrong needle causes more problems than people realise.

• Change the needle - if you can't remember when you last did, it's overdue; aim to replace every 8-10 hours of sewing
• Make sure you're using the right needle for your fabric - heavy fabrics need larger needles, delicate fabrics need finer ones
• Check it's inserted correctly - flat side to the back in most machines, pushed all the way up and tightened securely

This one catches a lot of people out. If the thread unwinds in the wrong direction it creates tension problems that cause snapping.

• Check the spool is sitting correctly on the spool pin - most machines have either a vertical or horizontal pin and the thread needs to unwind in the right direction for each
• If your spool has a notch, make sure it faces downward so the thread feeds smoothly
• Also check you're using the correct spool cap for your thread - the wrong size can cause it to unwind unevenly and catch

Even if you've already done it, do it again - slowly and carefully. A single missed guide is enough to cause repeated snapping.

• Raise the presser foot before re-threading - this opens the tension discs so the thread seats properly
• Make sure the upper thread passes through every tension disc and the take-up lever in the correct order
• Re-thread the bobbin too and check it's wound evenly and inserted correctly

Sometimes the culprit is hiding in plain sight.

• Look for any tangles, knots or snags on the spool or along the thread guides
• Check the thread isn't catching anywhere between the spool and the needle

Tiny burrs can form on the needle plate over time and shred thread without you noticing.

• Run your finger gently around the needle hole and feel for any rough spots
• A fine file can smooth minor burrs, but if the damage is more significant the plate may need replacing

Even a small build-up of lint can disrupt thread movement and cause snapping.

• Use a small brush to clear lint from around the bobbin case, tension discs and feed dogs
• Check under the needle plate if you can - lint accumulates there quickly

Sewing too fast puts real stress on the thread, especially on thick fabrics or with specialist threads like metallics.

• Slow down and let the machine do the work - your stitching will be better for it too

If everything else looks fine, tension is worth checking. Too tight and the thread will snap; too loose and your stitches will be uneven.

• Test on scrap fabric and adjust gradually until you find the right balance
• Start from the default or middle setting and move in small increments

Don't overlook the bobbin - uneven winding or the wrong type can cause thread to shred rather than snap cleanly.

• Check the bobbin is wound evenly - if it looks uneven or messy, rewind it
• Make sure you're using the correct bobbin for your specific machine - they're not all interchangeable
• Re-insert the bobbin and confirm the thread is pulled through the tension slot correctly

Before returning to your project, sew a few lines on scrap fabric of a similar weight. Confirm the thread isn't snapping and that stitches look even on both sides.