Basically slub is an effect as or a defect in yarn. Whenever yarn is over-drafted or under drafted or some foreign fibers mixed during spinning process then yarn is not suitable for making fabrics. This slub becomes valuable when we purposefully spin slub yarn with the help of SOG for making self created designs in fabric or Knitted Garments.
In early days copper wire brush was used to transfer the current, which was costlier and having little life so copper wires are replaced with Carbon which is comparatively cheaper and having long life but still it is known as Carbon Brush similar to copper brush.
No, Carbon brush are made as per requirement of application, hence it is having different size, shapes, hardness, material quality and grades etc. So it is required selecting carbon brushes carefully according to requirement of application.