Before working through the steps below, it helps to know which thread is actually snapping - this narrows down where to focus and saves a lot of time.

• Watch carefully or check the thread ends to work out which thread is breaking - upper looper, lower looper, left needle or right needle
• If you're finding it difficult to tell, try threading each path in a different colour - this makes it immediately obvious which thread is breaking when you run the machine

This fixes the majority of thread breaking problems on overlockers. Overlocker threading must be done in the correct order and even one thread slightly off can cause repeated breaking.

• Always thread the loopers before the needles - threading in the wrong order is one of the most common causes of problems
• Make sure the presser foot is raised before threading so the tension discs open properly
• Go slowly and refer to your manual rather than going from memory - overlocker threading paths are more complex than a sewing machine and easy to get slightly wrong

If any thread is catching or snagging on its way to the machine it will break under the tension of overlocking even if everything else is set up correctly.

• Make sure each spool is sitting correctly on its pin and unwinding smoothly
• Check the thread isn't catching, tangling or getting wrapped around the spool holder
• Make sure the spool caps are the correct size for each thread - too large or too small and the thread won't unwind evenly
• If your machine has a retractable thread stand, make sure it is fully extended - a partially raised thread stand causes the thread to feed at the wrong angle and can cause repeated breaking
• For nylon, rayon, silk or metallic threads, try using a spool net - these thread types can unwind unevenly from the cone and a spool net helps control the flow and prevent tangles above the spool

Tension that's too tight is a common cause of thread breaking on an overlocker.

• Reset all tension dials to the default or middle setting and test on scrap fabric
• Adjust gradually from there rather than making large changes - small adjustments make a big difference on an overlocker
• Focus adjustments on the thread path you identified in step 1

Poor quality or old thread is a very common cause of breaking on overlockers, which run at much higher speeds than sewing machines and put more stress on the thread.

• Use good quality overlocking thread - it's specifically designed to run smoothly through the looper system at speed
• Avoid using standard sewing thread on an overlocker where possible - it isn't designed for the speeds and tension involved
• Check the thread isn't old or degraded - thread that has been sitting on the spool for years loses its strength

A bent or blunt needle can cause the needle thread to snap, particularly on the left or right needle paths.

• Replace with a fresh needle of the correct type for your fabric
• Make sure it's fully inserted with the flat side to the back and tightened securely
• Check you're using the correct needle type for your overlocker - not all overlockers use standard sewing machine needles

A rough spot anywhere along the thread path can shred thread repeatedly, even if everything else is set up correctly.

• Run your finger carefully along each thread path and feel for any rough spots on guides or the needle plate
• Pay particular attention to the looper tips - a damaged looper tip is a common cause of repeated thread shredding and breaking
• If you find damage to a looper, it will need replacing - get in touch and we can advise

Once you've worked through the steps, test on scrap fabric of a similar weight to your project. Run a decent length of stitching and check all threads are holding without breaking before returning to your work.