DIN 6796 high-duty safe spring washers (HDS series) are designed for the connection of bolts. They are produced based on standard DIN 6796 and used to connect medium or high-strength bolts. HDS series are very useful for large bearing load and good elasticity resumption. The tension of bolt is able to endure the relaxation due to following: abrasion, deformation, relaxation, expansion due to heat, or shrinkage of wearing parts, or pressing of sealing parts. HDS series greatly increase the elasticity of bolts, can effectively substitute for conventional spring washers, but not suitable for combinations of locking washers or flat washers. HDS series of disc springs are applicable in an opposition or superposition combination. The opposition combination is able to increase the deformation of the pair of disc springs, while the superposition combination is able to increase the tension of the pair of disc springs. It’s better that they are pressed to flatness in assembly because this status will increase the tension moment, and then an appropriate bolt tension may be obtained without a torque wrench.