These Forgefix Flat Repair Washers have a large 40mm outer diameter. They are bright Zinc Plated for increased resistance to corrosion. Washers provide a smooth surface for the nut or bolt to bear on, making it less likely to loosen as a result of an uneven fastening surface. The primary purpose of a washer is to distribute the load under a bolt head or the nut face. Can be used with all types of bolts and nuts. Zinc coatings prevent oxidation of the protected metal to create a longer lasting finish. It does this by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not trigger a breakdown of the surface integrity as it is formed. The zinc oxide, if left intact, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers.