DESCRIPTION - Black Luster® Steel Metric Acorn Nuts provide best in class decorative appearance and better corrosion resistance than black oxide and zinc plated finishes. Resistant to 1,000 hours of salt spray per ASTM B117*. These nuts meet meet DIN 1587 & are also known as crown hex nuts, blind nuts, cap nuts or domed cap nuts. Acorn Nuts provide a decorative finished appearance with a domed top to cover and protect the threads.