It sounds like you're referring to 12-inch rack shelves. These are shelving units or accessories that fit within a standard 19-inch wide server rack or equipment rack, with the shelves themselves being 12 inches deep.

They are often used in IT, telecommunications, and other industries for storing equipment, tools, or small devices in a space-saving manner. These rack shelves are typically made of metal, such as steel, and are designed to support items like network switches, routers, or even servers, depending on their load capacity.

Is there anything specific you'd like to know about these 12-inch rack shelves? For example, are you looking for recommendations, installation advice, or dimensions?