Nylon bushings are bushings made of nylon or plastic like material. They are part of the internals of a mechbox that help holds the gears in place. Im AEGs that use lower FPS springs nylon bushings are fine, but in higher FPS AEGs that it is best to swap out the nylon and replace with metal. Since a heavier grade spring will degrade the bushing.
"Its only a little bit on fire"