Manufactured of carbon steel, cadmium plated per QQ-P-416A, Type II, Class 2. They provide a greater bearing area than AN960 washers. Used on wooden structures under both the head of the bolt and the nut to prevent crushing the surface.
Heard about Boelube for years. Finally had a chance to try it on several projects. It definitely works well and better than anything else I have ever tried. Would recommend.