Burndy introduced silicon-bronze bolts, nuts, and other hardware items on outdoor connector applications in 1927. Today the Durium trademark is a standard for this use. Durium bolts combine high strength with corrosion resistance. Bolts up to 2 inches long are fully threaded; longer bolts are threaded for two inches. Heads have American Standard dimension, and the threads are per American National Coarse Series, Class 2 fit. The silicon bronze is per ASTM B99.