Do I need special thread for an overlocker?

You do not need a different type of thread for construction, but you do need it in a different format and quantity.

Cones, not spools. An overlocker uses four threads simultaneously and sews fast, so it consumes thread roughly four times as quickly as a sewing machine. Cones of 1,000 to 2,000 m are the normal format, and a box of twelve is a realistic purchase rather than an extravagant one.

Ordinary polyester is fine for general overlocking. Overlocker thread is often slightly finer than sewing machine thread, which reduces bulk in a four-thread seam, but it is not a different material.

Woolly nylon — textured thread — belongs in the loopers. It spreads to cover the fabric edge completely, giving a soft seam that does not scratch against skin. Put it in the needles and you get a weak, spongy seam. This is the commonest threading mistake on a new overlocker.

Use cone holders or a thread net on cones that unwind too freely. Thread that spills off the cone tangles around the spindle and snaps mid-seam.

And match the colour approximately, not exactly. In a four-thread seam the loopers barely show, so a near match on the loopers with an exact match on the needles is standard practice and saves buying twelve cones per project.