I have seen normal, straight electro-magnet spiral coils and also doughnut-shaped toroid coils. This is similar to both ideas, but different. For on thing, since the iron core spirals around several times, an expanding electrical field from the copper wire cuts the iron core material more than once, so the magnetic field strength per amount of copper might be increased with this design.
It uses a long, flexible coil made by winding copper wire around a steel wool core. This steel wool increases surface area of the iron and may improve the magnetic field per amount of iron. That coil is then wound around a piece of PVC pipe to make an air-core coil. Nylon thread holds it all together.
The flexible steel wool core coil might be shaped in other configurations, too, for whatever reasons. I don't have the experience to know what they might be. If you do, let me know.