The Vitamix Retainer Nut is a critical component of every Vitamix blending container. It holds the blade assembly securely in place and features a rubber o-ring gasket to form a tight seal to keep water and food away from the blade. These newer Vitamix Retainer Nuts feature a black coating for easier cleaning and better looks compared to the older bare aluminum retainer nuts. They are currently made from zinc phosphate treated steel that has been powder coated for corrosion resistance. If you are trying to piece together a new container or just need to replace some parts, then you most likely need the Vitamix Retainer Nut. See compatibility list below.