Fits for a variety of mine carts. Helps reduce mechanical friction and reduce running resistance, improves the stability during use. Made from top quality cast iron, wear resistance, great vibration absorption, sturdy and durable, ensures reliable service. The outside diameter is 7 1/4 inch, the center hole is 15/16 inch. Used for making display carts, ensures the rolling stocks run and turn on the rails well. Will hold some weight, but not for everyday use. The outside diameter is 7 1/4 inch. The center hole is 15/16 inch. Made of highest quality cast iron. Wear resistance, great vibration absorption. Ensures long-lasting reliable performance.