Balance arm is a tool designed according to ergonomics, also known as positioning force arm (also known as positioning anti-torsion arm, counterforce arm, positioning bracket arm, positioning balance arm), mainly used in conjunction with the tightening tool, to achieve the sequence of screw tightening, to achieve the tightening process of the prevention of error and leakage, tightening data collection and preservation, reduce the operator's labour intensity and other functions. Enhance safety, productivity, improve the operator's working environment, to avoid the repetition of labour, excessive labour on the operator's physical health has a negative impact.