I have often been asked - can you only use designated serger thread in the serger.
You can use whatever thread will fit through the needles and/or loopers. I use regular sewing thread, embroidery thread, heavy decorative thread, jeansstitch thread, etc. Just remember to use a spool cap or horizontal spool feeder depending on the way the thread feeds off the spool. You can also run two or three spools into one or both loopers to create your own color thread. Just be sure the spools have freedom to feed the thread off. A few times I put them all in a bowl behind the serger and yippee I had a custom color thread. Always test stitch and go slow when you are trying something new.