For an electric tool, this is usually: spare contact brushes, which are erased during operation, since the material from which they are made by technical graphite. It is such a material that can provide good contact with the generator anchor, while not damaging the generator design during rotation. As for the cheaper tool, but, nevertheless, the appropriateness of its multiple use is quite justified, then in construction stores there is a sale of a spare configuration. A striking example: spare fur coats on rollers, in return for working manipulations in the process. To replace it is enough to know the size of the roller so that the seller can choose the right fur coat. From the intensity of work, rollers sometimes require several options for spare fur coats, so when buying you can choose the required complete set, since the choice of such spare parts is very large.