With three points of surface contact, these washers provide more stability than single-wave washers. They are curved and flexible to act like springs, compensating for tolerance variations and uneven surfaces. You can also use them to damp vibration.
18-8 stainless steel washers have good chemical resistance and may be mildly magnetic.
316 stainless steel washers have excellent resistance to chemicals and salt water. They may be mildly magnetic.