There are different kinds of discs that are used for various materials and tasks. Angle grinders can use grinding stones, sanding discs, wire brush wheels, cut-off discs, abrasive grinding discs, and polishing pads. Angle grinders come in different disc sizes and motor specifications. Other differences include a power source, rpm, and arbor size. Generally disc size and power increase together. Disc size is measured in imperial or metric units. Pneumatic grinders are generally used for lighter duty jobs where more precision is required. Electric grinders are more commonly used for larger, heavy-duty jobs.