Lost your marbles? Four Brothers offers round, high quality and durable replacement chromium steel balls designed for many popular and nostalgic games requiring 9mm balls. While these balls are designed to replace the popular Crossfire balls, they will work for any games requiring 9mm balls. Chromium metal is designed with maximum engineering properties that allow for a sleek and lustrous appearance in a gray metal. Never search again, as these replacement balls are known for their incredible resistance to corrosion and hardness resulting in a long-lasting product. These balls are NOT magnetic.