Sergers are available with various thread use options. You can create different stitches and different results with the number of threads you use on the serger. Again, this is an option that the more you spend the more options you will have.
A 2-4 Thread serger - This machine has the capabilities of a true safety stitch and a two thread overlocked edge. Two threads are used on each operation and you can use the machine to create each stitch separately from the other.
- A 3-4 Thread Serger - A machine which can function with 3 or 4 threads. Either amount threads will have a seam with some stretch capabilities, however a 4 thread seam, will give you a wider and stronger seam.
Most of these machines also have a rolled hem capability, by changing of the throat plate. For a rolled hem, the machine rolls the very edge of the fabric to the under side and encloses the edge with thread.
The 4 thread seam is sometimes refereed to as a "mock safety" stitch. It has much of the strength of a seam made with a Safety stitch or a separate seam but is not as strong.
- A 5 Thread Serger - This machine is in the expensive range but has all the seam capabilities you could want. 3 threads are used on the overlocked edge and 2 are used for the straight seam line. This is the seam you see on ready mades that have a overlocked edge with the straight seam having a chain stitch. When doing production work, this machine eliminate having to switch between machines for a strong seam and seam finish.