This part of ISO 603 specifies the nominal dimensions, in millimeters, of: — Type 1: Straight grinding wheel — Type 5: Wheel recessed on one side — Type 7: Wheel recessed on both sides — Type 20: Wheel relieved on one side — Type 21: Wheel relieved on both sides — Type 22: Wheel relieved on one side and recessed on the other side — Type 23: Wheel relieved and recessed on one side — Type 24: Wheel relieved and recessed on one side and recessed on the other side — Type 25: Wheel relieved and recessed on one side and relieved on the other side — Type 26: Wheel relieved and recessed on both sides. — Type 38: Hubbed wheel — Type 39: Double hubbed wheel These bonded abrasive products are intended to be used for external cylindrical grinding between centres. The workpiece and the grinding wheel are mechanically guided.