250mm (10 Inch) Flat Cut-off Disc B&H TOOLS CO., LTD. , https://www.bandhtools.com Multi-key connection is used to transmit the shaft with high torque. In order to balance the force of each key, the position accuracy requirements of each keyway are proposed. For example, the symmetry requirement of the screw for the production of the screw is 0.025mm. The indexing is not up to the required level. To this end, we have studied and designed a symmetrical keyway machining control tool. To control the degree of symmetry, two conditions must be met. One controls the error of 180° in the two keyways.