Solid Sterling Silver Rhodium Plated 4mm Bismark Chain Necklace, 16" 18" 20" 22" 26" Unsure what length chain to buy? 18 inches is the standard length and will look great on most people. This necklace is made of solid rhodium plated sterling silver and stamped "925". This classic necklace looks great alone or with your favorite pendant. Necklace is 4mm thick and comes in: -16 inch long ( weight: 9.7 gram); -18 inch long ( weight: 10.9 gram); -20 inch long (weight: 12.1 gram); -22 inch long (weight: 13.3 gram); -26 inch long (weight: 15.7 gram).