under what circumstances should choose flat washer or spring washer
1. When increasing the contact area between the screw and the machine, a trim pad is required.
2. To eliminate the damage to the surface of the machine when the spring washer is unloading the screw, a flat washer is needed. It must be a spring washer and a flat washer when used. The flat washer is next to the surface of the machine, and the spring washer is between the flat washer and the nut.