6pcs well nuts are made with brass and rubber sleeve, great accessory for your kayak, canoe, boat. Specifications: Material: Rubber + Brass Size: M4 / M5 / M6 (Optional) M4 Dimension: 13 * 11mm / 0.5 * 0.4in M5 Dimension: 17 * 14mm / 0.7 * 0.5in M6 Dimension: 21 * 16mm / 0.8 * 0.6in Package List: 6 * Well Nut (Screw is NOT included)