The primary purpose of spring washers is to provide tension and preload in a joint assembly. This helps to maintain clamping force and prevent loosening or loss of tension due to vibration, thermal cycling, or other factors. Plain washers are flat, whereas spring washers are curved. For most applications, plain washers are typically used. For machines and objects that vibrate, spring washers are recommended. Spring washers are unique because they provide an axial load that counters vibrations and, thus, prevents fasteners from loosening.