These are flat washers with a particularly large outside diameter in relation to the hole size. They are commonly used to spread the load across the fixing material. Also known as penny washers, mudguard washers or fender washers in the USA.
Stainless steel does not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high salinity, or poor air-circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties or steel and corrosion resistance are required.